Because most lenses do no have a fixed aperture, do most photographers avoid using zoom as to avoid messing up their settings and their established exposure?
do most photographers avoid using zoom
If "most photographers" avoided zoom lenses with variable aperture, there'd be fewer zoom lenses with variable aperture on the market. Furthermore, there are plenty of fixed aperture zoom lenses available at a range of focal lengths, so it's safe to say that photographers don't have to avoid zooms just to have fixed aperture in most zoom ranges.
I suspect that by photographers you might mean professional photographers, but even so, different photographers have different priorities. Are you talking about sports photography? Landscape? Portrait? Fashion? Photojournalism?
avoid messing up their settings and their established exposure?
I don't think this is a huge priority for "most photographers." When you zoom in or out, you're changing the shot significantly anyway; considering exposure again should be part of that process.
Most photographers will weight various factors to get a particular shot. If you can't get the framing you want while zoomed out, you'll zoom in. But if that changes the depth of field (because the aperture is now f/4.5 instead of f/2.8, or whatever), you need to weigh how important depth of field is to the shot. (Or don't weigh it, take the shot anyway, and see how it turned out.)
It's like any other parameter on a camera. You don't give up on a fast shutter speed just because there's less light. You compensate with a wider aperture or a higher ISO, or by adding your own light if the shutter speed is really important. Or, you try at a slower shutter speed and see if you can reasonably get the shot, or perhaps get a different shot that looks better at a lower shutter speed.
If you want to keep your aperture wide open and your lens doesn't allow it at closer zoom levels, you either move closer (zoom with your feet), zoom in anyway and deal with the larger depth of field, or compose the shot differently. It's all about choices. But I don't think most photographers are avoiding zooming very often.
I think zooms are even more popular than ever with photographers. The optical quality of even a modern kit zoom is so good that it's often hard to justify using a prime, unless you specifically require a wider aperture.
The "fear of zooms" comes from the period long ago when most cheap zooms were considerable optical compromises for a serious photographer and when even the cheapest film SLR often had a 50mm f2 attached by default.
Those days are gone.
With the combination of really excellent high ISO performance on even the cheapest DSLR and good optics of a modern kit lens, it's often hard to justify using anything else.
I'd say the primary concern is composing the shot, and making the composition fill the frame. Exposure then follows on from that.
Composing the shot involves repositioning yourself and the camera, and filling the frame involves selecting the appropriate lens OR using the zoom.
If you don't have a zoom, then you're into switching between primes. Would all your prime lenses have the same maximum aperture? No, so if the choice of exposure settings is critical you'd need to reconsider/adjust them after you frame the shot.
Most people don't worry about it. We know this for sure because a) zoom lenses with variable max aperture are pretty much the only option on compact / point and shoot cameras without interchangeable lenses, and those are wildly popular, with ever-increasing zoom range as a selling point, and b) when you get to interchangeable-lens cameras, lower-cost zoom lenses are again the most popular by a wide margin.
And, again for most people, that's perfectly reasonable, because for most lenses the difference from the extremes is only a stop or so, and that means that if you're shooting in an automatic mode, changing ISO or shutter speed handles it just fine. It's a little annoying when in low-light situations where you're hitting the limits, but there it's mostly just annoying that the lens is slow, not that it's a little faster when zoomed out.
One might make the argument that these mass-market consumer picture-takers aren't Real Photographers, and therefore don't count. But that's not so. Because these basic zoom lenses are so low cost, and the quality of manufacturing relatively high even at that price, they are a very good value, and are popular among working professionals and serious enthusiast photographers as well.
Sure, there's a tradeoff, but it's a narrow one. Even if you are using manual exposure, it's only an issue when you're at the wide end of the aperture anyway. In many cases, you'll be at f/5.6 or beyond anyway.
But that said, many people do avoid zoom lenses with variable maximum aperture. See What are the advantages of a lens having a fixed maximum aperture? for a whole Q&A on the topic, but overall it's telling that almost all high-end zooms keep the maximum aperture constant throughout the range. (More discussion on this at How do constant aperture zoom lenses work?, too.)
And, to get very specific, all of this is certainly a factor in some people avoiding zoom lenses. It's not my only reason, but it definitely contributes to the fact that I don't own any zooms and haven't for the past almost decade. Those high-end constant-aperture zooms aren't just expensive — they're also big and heavy. For the price and weight, I can have a number of really nice, fast primes instead. I'm certainly not arguing that this should be the path of all photographers, or even what you do, but if you find that this does factor into your concerns and equipment preferences, don't be ashamed.
When time for taking photo is short, most photographers use AE (automatic exposure) - so changes in aperture are instantaneously compensated by shutter speed. Manual exposure is typically used in very controlled environment (eg studio) when there is plenty of time to re-adjust the aperture anyway.
So to answer your question: no, under typical conditions changes in aperture are not a noticeable issue. Unless you deliberately create a problem, eg by shooting manual in rapidly changing conditions.
There are a lot of feelings of inferiority amongst photographers, thus there is a lot of posturing amongst photographers.
There was a time (and it still occurs) where photographers would claim that "they don't use zoom lenses because primes are so much superior". "I zoom with my feet" was a common phrase. There was probably a time where this was true, but the sentiment has lasted long after the zoom hardware has improved.
You may also remember this sentiment regarding auto-focus and auto-exposure and well, just about every new development.
Humans are complex, so there are many other reasons why photographers avoid change. I remember the rumblings of moving from view cameras to 4x5, and 4x5 to 35 mm. I'm sure there were many heated exchanges between those that refused to switch from glass plates to film.
The best equipment is the stuff you have with you. Go have fun and take pictures. If you're happy with your pictures (or even if you're not) don't get sidetracked with other photographers telling you how you're supposed to be taking pictures.
Its mostly about money. Most of us use what we have. You can buy very good constant aperture zoom lenses, but these tend to be much more expensive.For example the constant aperture 70-200mm f/2.8's from Canon or Nikon cost over $2,000.00 or the Sony over $3,000.
Since I have an old nikon DSLR, if money were no object, Id buy these two lenses: the 24-70 (constant) f/2.8, and 70-200 (constant) f/2.8. These are spectacular lenses, but the set would cost you about $4,000.00 for the set. And maybe I'd buy a Zeiss Otus 85mm f/1.4 for portraits (this one is $4,500.00). For pro's, it might be no object, but for most of us shooting our kids soccer games and family get togethers, its out of our price range.
For most of us mere mortals we get a camera kit with a cheap kit lens like the 18-200mm f/3.5-5.6, and suffer with not enough light even in many daylight situations when zoomed at the tele end. This lens is about 600.00 if you shop around. And for portraits where you need more light, you could get a $220.00 50mm 1.8. These are both cheap, plastic kit lenses, that are not nearly as sharp as the pro versions costing up to 10x more, They will fall apart long before you're tired of them, and they don't render colors very well. But most of us are not shooting cover photos for glamour magazines.
Back to your original question: if you're shooting a soccer game, and all you can afford (like me) is a cheap kit zoom, then that is what you use. I have a cheap 50mm fixed lens, 220.00 but no way can I reach across the soccer field with that lens, although it does have a wide aperture of f/1.8. The cheap zoom lens I have runs out of light in most situations, even in daylight, zoomed to the tele end, the best it provides is f/5.6, so I have to jack up the iso, and deal with the grain. Around the house, or closer shots, I can use the 50mm but composition is a pain, and sometimes you just can't back up enough to get the shot, e.g. if you're inside the house.
do most photographers avoid using zoom as to avoid messing up their settings and their established exposure?
No, because in certain contexts where versatility and speed of operation are needed, nothing can beat a zoom lens. But many professional photographers do use constant aperture zooms for the reason you mention and others (the fact that constant zooms are generally relatively fast, i.e. f/2.8 or f/4, is obviously also a big incentive).
There is a sentiment that photographers use prime lenses. This is correct to a certain extent for portrait photographers and people doing studio work. Yes the best glasses are prime. So it is correct what you are alluding to.
However, there are many fields where zoom is very important. For example shooting wildlife. Though there are lot of photographers who use prime, still there are so many who vouch for zoom. For zoom helps to track the animal when they are moving towards are away from you.
So broadly speaking no they do not. Their choice is based on best glass available rather than the presence or absence of zoom.