It doesn't matter if it's a dangerous cult. Scientology is a dangerous cult. It isn't illegal.
What people believe cannot be illegal. What people do, can. The entire basis for law in a free society is that nobody has the right to dictate what to think, but also nobody has the right to use force, except in self-defense. People's rights end at the point their actions become violence or force, but not because of what they believe.
At the same time, I think as a nation we have every right to only allow entry to people that share the same base values of freedom and individual rights. At this point the doctrine of Islam does not.
There is a component that advocates the murder of non believers. That’s criminal and should be accepted as such.