Expression of thoughts can definitely be a crime. Saying that you support X Y or Z organization or ideology can definitely see you jailed.

There is also a trend, even in the US, towards keeping some prisoners behind bars for thinking certain thoughts. Sex offenders in many US states can be held long after their sentences based on mental health determinations, determinations that turn on their response to questions: their thoughts. Whereas expression of thoughts can be clearly illegal (ie hate speech) simple consumption, reading, of such thoughts can land the reader in jail too. Governments aren't yet crawling into people's heads, but they are certainly willing to criminalize the communication of illegal thought.