Politeness can be good manners because it makes someone feel good. Just because you make a person feel good doesn’t mean that you were genuine about it. Politeness is a way of making someone’s day. For example you say “oh your sweater is pretty” just to make their day that does not mean that you were actually telling the truth. Maybe you just want to make the person feel special because everyone else didn’t. Let’s say everyone at school was bullying this guy about his haircut and just to make him feel good you told him it was nice. Therefore, politeness can be half good manners and half a lie. Don’t get me wrong sometimes people can genuinely mean it but think about it every time you were polite to a person atleast one time you were just doing it to do it, you weren’t genuine about it.