A horde of trailer-park visigoths can sack the Capitol and Republicans say "what's the big deal?" But let one guy show up in casual clothes and they lose their goddamn minds.
I think this is fine. I understand why rules of formality exist, but it's not like Congress shows decorum in its actions. If they want us to respect it, they should pass good policy that helps people, we care much more about that than whether individual senators wear a suit.