As nice as it would be to not have to see ignorant youngsters with T-shirts depicting mass murderers, I don’t like this for 2 reasons.
1. If something is taboo, the general public is deprived of the possibility to see how idiotic it is.
2. “I disapprove of what you say, but I will defend to the death your right to say it” is a great principle and applies to this subject as well.