Conspiracy to commit foo, is illegal for many foo. So, it is illegal to fantasize out loud.

That isn't how conspiracy to commit works. There has to have been foo (or an attempt at foo), and demonstrable knowledge of that act of foo (or highly probable knowledge), and actions to further the committing of foo (direct or indirect I believe). Just exploring stuff in the hypothetical is completely legal.

Only if you take real action towards committing foo. Talking about it does not constitute real action.

Conspiracy to commit foo generally means you are planing to commit foo, not talking about the best way to commit foo.

It is illegal to attempt to blow up the bridge. But if you do so when led by an agent of the state, having been convinced by an agent of the state to perform the act, and with the necessary materials provided by the state, then you ought not be convicted of a crime.

The more worrying part of this article is the targeting of certain groups and certain ideologies. Even if this particular case wasn't entrapment, that the FBI is specifically targeting certain groups and egging them on to commit acts of violence, is undemocratic and just plain evil.