Why do liberals get all pissy when people protest against radical Islam?

I believe that not all liberals are trying to quash criticism of radical Islam. A anyone can see, radical leftists have a lot in common with radical Islam. For example, both groups are intolerant of opposing opinions. Both groups deplore the existence of Israel. They both hold their beliefs unquestioningly and listen only to those whose fervor matches their own. Both groups harbor and protect their most violent members and seek to justify the violence based on their strongly held beliefs. So, their is a kinship between the radical liberals and radical Islamists. Birds of a feather, I guess.