I'm sure they would try to turn away any middle class homeowner who hasn't bathed in months as well.

I think it's reasonable to have some sanitation and pleasentness standards in a restaurant. Anyone from any economic class could meet or not meet those standards. It may be harder for a homeless person to stay relatively well kept, but I don't think that is the responsibility of the restaurants to fix. We should reduce the people living in filth, not accept and encourage filth I'm public spaces.