If I'm following your implication, I think this is less of a slippery slope than you think. When one's ideology is organized around killing people based on the color of their skin, it deserves no space in modern society.
"Thought crime" comes from Orwell for me. Except his meaning was probably a bit different than I thought.
Anyway I define it as criminalizing certain expression of ideas in a violent attempt to control what population thinks. Also you're reacting to Thailand story, so I'm not sure what American right has to do with this.
I'm merely trying to give a possible explanation for codydh's reaction. Searching "thought crimes" for example on Google news also shows how the meaning appears to have changed.
Also this discussion started with somebody asking what they can do to help, given that Thailand is far from our sphere of influence.
In your response of "Find and support people who are against persecuting thought crimes within the country", the "within the country" could be easily interpreted as whatever country the people discussing are in, which will likely be some Western democracy. So I believe your statement can easily be interpreted as trying to make a connection between free speech issues in the Thailand and the 'fight to free speech' of the alt-right in Western Democracies, asking for tolerance of their intolerant opinions (this is not just a US phenomenon btw).
Note also how the example of Chinese tourists getting arrested in Germany for making the nazi salute is used as a suppossed freedom of speech issue in this thread. A news article about that was actually one of the first results in the google search for "thought crimes" [1].
