I know it's POPULAR to call conservatives DUMB and while I don't like to beat dead horses, I really think the explanation for this is that they're DUMB. The ILLITERATE form of dumb, to be precise. The caps are a way of adding EMPHASIS - which is something that can ALSO BE DONE by PHRASING, WORD CHOICE, SENTENCE STRUCTURE, and so on. But those techniques would require a beyond 4TH GRADE level of writing and reading ability, so they do not succeed in the conservative communication MARKETPLACE.

I will add a disclaimer, my beloved Nietzsche also does all caps words SOMETIMES, but I believe that since this is alongside his impressive ELOQUENCE, it is clearly not a sign of stupidity in that context. Likewise, it is not a sign of STUPIDITY in many other contexts. That is to say:

Using that style of communication does not ALWAYS make it a safer bet that someone is stupid, but being stupid does make it a safer bet that they use that style of COMMUNICATION.

I think philosophers around that time often did this especially if they were using a word in a way it is not usually used.