It isn't necessary. In fact sometimes the photo is all the better when the subject isn't looking into the camera.
Here's the deal: No matter what you do if you put your photos out in the wild in places where they can be critiqued someone will have issues with the decisions you made when taking the photo.
I'm sure there are critics who would find fault with Ansel Adams' "Moonrise - Hernandez, NM"! I'm sure there are plenty of wanna' be photographers that think Walter Iooss, Jr is a hack and that with the access he has had they could have captured better images! Steve McCurry's 1985 National Geographic cover photo of a green eyed Afghan girl probably has detractors as well. Simply put, you can't please everybody. The only person you should be concerned about pleasing with your personal photos is... yourself. Study the masters, learn the "rules" of composition, realize for every compositional rule out there someone has done quality work by intentionally breaking it, and then go out and shoot the way you want your photos to look!
