Pretty hard to do that when the beliefs explicitly endorse murder. Ziz used to run a blog on which she made thinly veiled death threats, argued for a personal philosophy of hair-trigger escalation and massive retribution, raged at the rationalist community for not agreeing with her on that philosophy and on theories of transness, and considered most people on Earth to be irredeemably evil for eating meat.

This is a free country (disputably) and you should be able to think and say whatever you want, but I also think it is reasonable for law enforcement in the investigation of said crimes to also investigate links to other members in the movement.

It doesn't work. Every single time a radicalized member of the marginalized community does this kind of crime, the numbered-letter-agency dutifully reports, that they knew the person to be radicalized, but had nothing to act on, because a lot of people have weird violence-approving beliefs, talk about them openly or with friends and very few actually hijack a Boeing or two. Those who plan to do things also happen to learn about op-sec mistakes of those caught before them.

Israel knew about Hamas, and the russian empire of 19th century knew about anarchists. Pouring a lot of resources into suppressing all of that didn't do jack shit in the long term.

There are hundreds of thousands of rationalists (to a greater or lesser extent). Very few go shoot people.

Cops can do a lot without it. They can choose what leads to follow.

But not sure what you are suggesting with respect to wiretapping.