For me the most annoying aspect of "displaying intelligence openly" is the following:

Imagine that you have an average person A, an intelligent person B, and a super-intelligent person C. More precisely, imagine that there are 100 As, 10 Bc, and 1 C, because most people are at the center of the bell curve.

From A's point of view, both B and C are smarter than him, and he cannot really compare them. All he can say is that he kinda understands what B says, but a lot of what C says is incomprehensive.

The experience of B is that most people are either A or B. Add some political or other mindkilling, and B may quickly develop a heuristic "everyone who agrees with me is a B, and everyone who disagrees is A and a huge waste of time".

Now once in a while B and C meet and disagree about something. B, using their long-practiced heuristics says "lol, you're an idiot".

An observer A looks at their interaction and thinks "B is probably right, since I know B to be a smart person; and C also seems kinda smart, but not as smart as B, and B says he is wrong, so he probably is".

From my point of view, B is "cheating" in this process, using both his intelligence and his lack of even higher intelligence to create an advantage over C. Thus I applaud the norms which prevent this, even if they were created for other reasons.