The beauty of the Constitution is that it allows for the freedoms we have. Some groups and ideologies run contrary to Constituitonal law, including Marxism and Islam. I had a coworker try to tell me that my concerns about Marxism/Socialism in this country are unfounded because there has not been, nor will there be, a physical, tangible working class revolution. I say the most effective revolution is one that happens right under everyone's noses so that people don't realize they have been fooled until it is too late. Hitler took away Germany's right to bear arms in 1933. People should be worried about 2000+ page congressional bills that are not read, regardless of party affilliation. The head of the socialist party in the 1930s said that Americans would never accept socialism unless it was disguised as "liberalism." A Socialist prophecy came true, if I may mix a few beliefs together.
Yes, there are two sides of the coin to religious freedom. Things I may disagree with are allowed, but so are the things that I do agree with. If others want to enjoy the same freedoms I have, then great. Come on over! But if others want to take away my freedoms because they run contrary to their beliefs and ideologies, then I have a problem with that. The rattlesnake is still a rattlesnake. Hard words, but true words.
The evidence you seek is in the Islamic practices around the world. Women are still stoned to death and people are still beheaded. Muslims rape non-Muslims in the Sudan, let alone all of the killing. Not all groups fall into the "extreme" category as we put it, but, correct me if I am wrong, few, or no Muslim groups speaks out against these more extreme Muslims. I say this because I believe they have the same fear of physical retaliation as do non-Muslim groups. They are afraid to speak out and have no freedom of speech, even responsible speech.