I don't think they should be banned, but prepared to be pointed at or looked down on. If you have no problem with that, go for it.
You aren't going to be taken seriously by other parents or the school though.
What if there was no dress code for the kids at school. Do you think it would be okay for kids to head out to school in Pj's and slippers?
My high school didn't have a dress code and as long as your clothes didn't say anything obviously sexist or racist you could wear it. So when the pajama look was in the students wore pajamas to school. I hated it, but it was within the schools rules so all I could do was sit back and hate. I also hate flip flops, but I have to do the same thing now whenever I see people wearing them.