It's... still an incredibly bad idea. Magic is secret.

You can much more easily excuse breaking a guy's arm as something mundane then pulling out a magic sword and hacking his arm off. In the afternoon. It's not actually night yet.

I mean, it's not like a villainous character couldn't go killing civilians but they'd need to have some sort of logical reason and be more subtle about it then just murder in the middle of somewhere anyone could see.