Not sure how arguing against a police state is a liberal idea? In fact I'd think arguing that one should be able to live their life without fear of the thought police dropping the hammer on them is a pretty conservative argument.

If someone breaks federal law I hope the FBI nails them. But short of actually committing a crime I'm not sure what any LE group can do about it.

We can't police intent without first suspending civil rights.

LE investigates crimes they don't prevent them. And arguing that they should be stopping them is an incredibly scary thought to me that could spin out of control extremely quickly.

Not sure why that is so difficult a thing to understand. Your argument is sound right up until the time you are the target of that argument.
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"Government does not solve problems; it subsidizes them." Ronald Reagan

"The trouble with Socialism is that you eventually run out of other people's money." Margaret Thatcher.

"How fortunate for governments that the people they administer don't think." Adolf Hitler