Given people will give their life and take other lives for a religious cause, it is clear that that is illegal from the individuals stake and illegal for a religious leader or organization to promote the act. A violent branch of a religion should get a different name and a different status and be clearly identified as illegal, not a religion, and lawfully dismantled. It is in no one's interest to have extremists committing crimes and to promote it under the guise of "God's will" is not something we can stand as a society. Given the society must benefit, protecting organizations that promote violence as free speech is not allowed, and should be expressly outlawed in the case of religions.
No one wants to be on the receiving end of violence so sence nobody wants it yes it should be illegal. You wouldnt want your country to be invaded and your women and children to be enslaved so you shouldnt be able to do these things either and any religion that promotes what nobody wants should be illegal.
In the perfect society education would push people away from religion, many religions are violent and full of hate, hating them back and pushing them to the underground would only bolster their views, the fact that they would be persecuted would only make the religion more appealing to some people,
at the end of the day it is people who are inherently violent, religion only furthers this, education and love alone can solve this.
We are constantly trying to make things legal, like gay marriage or recreational drugs, so why take regressive steps like this?
Religion is archaic anyway, we should abandon it, any not pay it any attention, we should all think for ourselves and not be sheep.
In the perfect society nothing would be illegal, not even murder, because everyone would be well educated enough to know the difference between loving someone and harming them.
Outlawing an entire religion is a ridiculous idea anyway, since when has banning something made it less popular?
Never, people just want it more.
Most often, major parts of religions do not encourage violence, only a small part or branch of it does. It is unfair to outlaw an entire religion simply because a certain branch is being violent. Also, people have religious freedom. It is a problem if they violate the law and do violent things, but it is technically not illegal for them to believe in something violent. If not, video games fan groups could be outlawed as well...