Context
Why... acceptable while... frowned upon by the photography community?
The context changes what is acceptable and what isn't. The context of your original question was "traditional photography rules" not "photography community". But what is photography community? Everyone who owns a camera? There are so many subgroups with contradictory preferences that it doesn't make sense to ask about the preferences of the entire group as a whole.
Nature photographers are expected to photograph nature, not caged animals or taxidermy specimens. Documentary photographers are expected to represent reality as nearly as possible, not to airbrush people out of photos. No such restrictions apply to ordinary people.
In my previous question someone pointed out that unnatural HDR based toning will get more objections from the photography community than cropping.
By the numbers, far more people will object to the HDR toning than to cropping. Anyone who objects to cropping is likely to object to the use of HDR toning. Many people who find cropping acceptable object to HDR toning.
Your previous question was about "traditional photography rules" (whatever that means) and cropping. While cropping has a long history and can be justified as falling within the bounds of "traditional photography" (whatever that is), HDR toning is a recent development that is far less likely for anyone to consider more "traditional" than cropping is.
HDR Toning
It's very much like looking at impressionistic patinings. The execution is at least as important as style choice. Some nice images have been created using HDR, but the effect has been over-used. Many people are now tired of it. There are also images where HDR is not well used. This includes images with lifeless colors; halos; desaturated, low-contrast shadows; and exaggerated, over-sharpened details.
Hardware vs Software
Why is hardware based manipulations... acceptable while software based manipulation... is frowned upon...?
As others have mentioned, the distinction between "hardware" and "software" isn't clear because modern cameras are specialized computers. Most cameras have multiple toy modes, and some cameras have in-camera raw processing, along with other editing capabilities.
Restrictions to limit photography to in-camera processes might have originated as a guideline for documentary photographers to reduce the temptation to edit their photos. For some, it's a point of pride to get it "right" in camera. For others, it's a time saver to not have to post-process.
Eye of the Beholder
I personally feel that slight HDR based enhancements are OK from an artistic perspective...
You can do whatever you want and call it art. You don't even need a camera. Whether other people agree with your "artistic" tastes is a different matter.