There is a decent argument historically that communism and other left movements are extremist, racist, and anti-lgbtq. When you start banning concepts, you open your communities up to several things.
Group think
Banning of other radical ideologies that you may agree with
You alienate those people from exposure to better concepts
You jump start compaction cycles for large scale propaganda organizations that could lead to actual violence
There is a decent argument historically that communism and other left movements are extremist, racist, and anti-lgbtq. When you start banning concepts, you open your communities up to several things.