I can only speak for my part of the state, where we are mostly rednecks (according to the rest of the state).
The people who would be considered as not looking professional, if they wore tennis shoes, while representing their chosen "profession" in no particular order:
New car sales people
Used car sales people (if affiliated with a new car dealership)
Clerks in up scale department stores (except the fad and teen stores)
Bank clerks (excluding fad and teen banks)

Bank managers
Attorneys
Attorney's receptionists
Funeral Home employees
CPA's
Accountants
Investment consultants
Hotel managers
Hotel clerks (in most any hotel that costs more than $41.25 per night)
Restaurant managers
Please everyone, put on your humor cap when you read the descriptions above.
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Lest there be any misunderstanding (good luck with that, huh?), I realize at weddings the photographers are on their feet for hours, but in my opinion there are alternatives to extremely casual attire. "Semi-dressy" shoes are available that can be worn with suits.
I dress for the occasion. In my studio, I photograph a lot of high school age people and I wear jeans, and leather casual shoes. If I go out to an oilfield location, I wear boots, etc. If I photograph an executive I wear appropriate attire, usually a sport coat, etc. I assisted at an event for the Bush family, and I certainly would have felt out of place in sneakers, or jeans for that matter.
I am not telling anyone how to dress. However, when I photographed weddings, I did have some people tell me that they selected me , over a competitor, because I looked professional, as well as my work.
As I mentioned before, there used to be two video guys who wore sneakers to weddings. No one really complained to their face, but I heard many tell me they would not use them because they looked as if they didn't respect the occasion.
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As far as my comment about bare footed... Well, naturally if you are at the beach that is different. But it looks a little back woodsy for a photographer to go around in bare feet at a country club, and that is what I meant.