How could you let this thing happen in your religion? How can you be a member in the same club as these fuckers?
I'm not sure that either of those is actually a fair question to ask anyone.
Just as a thought experiment, imagine that there were several groups of militant atheists out bombing churches, mosques, and synagogues around the world, claiming that they were doing it because they were atheists, and all religious people needed to drop their delusions or die. How would you justify being "a member in the same club" as people like that? How would you answer, "How could you let this thing happen in your group?"
The former question is assuming that just because they happen to share some relatively broad affiliation (and yeah, "Muslim" is a truly absurdly broad affiliation; there are more Muslims than there are Chinese people in the world), they can somehow prevent these people from doing terrible things and claiming they're doing it in the name of that affiliation.
The second is assuming that because these things are being done by what are, if you do the numbers, really quite tiny splinter groups of the main affiliation, that all 1.6+ billion other Muslims would renounce their religion and...I dunno, turn atheist?
Basically, what, exactly, is it that you expect the 90+% of all Muslims who don't know any Islamist terrorists, and don't know anyone who knows one, to do about this that you or I couldn't do just as easily?