I don't really know what you're talking about... of course there were large mass demonstrations in the US after the election of GWB and to my memory they didn't sentence hundreds of demonstrators to death after their arrest ?
But I might have to use the term militant left instead of extreme left, and I believe they are by far less oppressed than the militant right for example, and every year they can riot without any major oppression by the police at all, just reaction when the riots start. They always try to deescalate, not provoque, stay out of sight etc etc... And give them plenty of free space to do whatever they please, just like in Geneva.