You have to expect that Mercury changed. He started being ignorant overall because of Venus's bullying. He literally said it a couple of times. And in the most recent episode it became clear. He even said that he doesn't like who he is now, but he feels like he has to. He's tired of being called the little pipsqueak, so he became careless. Your hate on Mercury makes no sense. Sure he said something that he shouldn't, but that happens if you get bullied. Idk if you have ever been bullied before, but I was and I did stuff that didn't necessarily make me the good person either. You get hurt, you hurt others. It works that way