I don't recall saying there was a sin. When I say, "shouldn't," I mean "shouldn't if you want to be excellently dressed." I am talking about principles for excellent dressing, not principles for non-ugly dressing. It's a question of what is excellent and what non-excellent, not a question of what is acceptable and what sinful. I haven't yet accused anyone of ugly/sinful dress. SF has changed since I joined. I find it strange that a lot of people here now seem to think there's firm rules for what's acceptable, and so long as you follow those, then whatever floats your boat, bruh! In the real world, there are many waystations between the ugly and the excellent. It's like the difference between Vass and Allen Edmonds. Both make good shoes of honest quality. But no one who knows anything about shoes would say that AE's shoes are as good as Vass's.
There is no such thing as principles for excellent dressing, there are only principles for good dressing. Excellence is beyond rules and principles.
Like if you have some talent and go to good painting academy, you will learn principles and become good painter. You can learn and practice principles as much as you want, you might never become excellent, as in one of the great painters we all admire. And some of those actually found excellence by breaking rules.