My DD had her 3rd party at maccas (shock horror!) so obviously I don't see a problem.
To me party time is time to eat crap etc because regardless of where you have a party you are pretty much going to be eating crap.

secondly the happy meals do offer options, you can get chicken wrap instaed burger or nuggets and apple slices over chips, water for drink.

Yes my kids do see the golden arches now and ask for chippies but they know its only for every now and then not a regualr thing. To us its about moderation.