Well supporting political views from modern history can have such effect! Specially when they are at the losing side and have branded with major evil acts.
The fact that such banners causing trouble isn't because we suppress the freedom or anything like that. Is simply because it will start major conflicts between people who support for their reasons the opposite sites. Because many find it insulting or provoking.
Also note that games, as Wolfenstein (not the 2009 version) where banned or released with altered versions to several regions of the world removing "evil" symbols or references.
If you would like to talk about such issues or history (by being really careful) I would be glad since I love WW1-WW2 eras...