I don't think the solution is for the government to regulate which religions are considered fundamentalist and ban them for infringing on people's freedoms. To be honest, I have no idea what the solution is.
Ironically, the solution is the one we already have.
We have therapists that help with cults for people who may want to leave. I may suggest making them as openly available as the sex trafficking posters in public bathrooms, but the freedom to have a personal religion will always come with the cost of stupid or naive people. Going too far in either is a bad idea. We saw what the USSR did to rid religion and that only made stronger cults. Cults THRIVE on persecution, so the best thing to do is make them feel as welcome as possible so it defys their belief.
Almost every cult commits some form of crime as well. From money laundering, to child sex trafficking, slavery, or scams. The ideal method to weed them out is to watch and wait for the heads to fuck up and get caught, because they will.