"Culture" is just a set of practices and assumptions that have been internalized - talking about where they came from is anthropology/history. You can certainly have conspiracy theories in there, but you seem to have confused those with any explanation at all.

(As for shaking hands - it seems to be pretty well established that it is a way of showing that you aren't going for a weapon - https://deepenglish.com/2014/07/handshake-history-listening-...)