Well, the extra "that" before "that it actually" really doesn't help matters. I've tried to make it slightly better but it still seems to be a bit convoluted.
Thiss?
There's a related problem: Once they have terms for something, humans have a tendency to take for granted that anything that appears to make superficial syntactic sense actually has semantics behind it.
Or just use a bunch of commas?
There's a related problem; Humans have a tendency, once they have terms for something, to take for granted that something that looks, at a glance, to make rough syntactic sense actually has semantics behind it.
[I'd put this in an open thread, but those don’t seem to happen these days, and while this is a quote it isn't a Rationality Quote.]
— Geoffrey K. Pullum, Language Log, “Never fails: semantic over-achievers”, December 1, 2011
This seems like it might lead to something interesting to say about the design of minds and the usefulness of generalization/abstraction, or perhaps just a good sound bite.