It's your decision whether to allow your child to do something or not. I don't know what you mean by 'harm' but it sounds as though the McDonalds party wasn't a good experience for your DS so he probably won't mind if he didn't go to one ever again.

I wouldn't be offended at all if someone declined an invitation because they don't like McDonalds. Acutally, I wouldn't be offended if they declined an invitation without a reason. I don't get all narky over birthday parties. Your reason is a valid one though. I wouldn't allow my kids to go to a birthday party at a circus because it goes against my way of thinking, your stance on Maccas is no different to that in my eyes.