I think it shows disrespect because they will most likely be dressed up and you won't. And I'm talking about the situation when you need something from them, like a job offer or investment. It doesn't take any more effort to throw a polo on as it does a t-shirt, so the fact that you chose the t-shirt, I believe that's disrespect.

Just tradition? Yes. But traditions exist for a reason. Sure some people in Silicon Valley may be cool and just care about your brain, but the rest of the world doesn't work that way. Try going to an interview wearing a Simpsons t-shirt and shorts and just try to get treated the same way as if you were in a suit.

With all due respect, I don't think you've offered any kind of explanation here.

Why is it more respectful to be dressed up if they are? You've simply restated that it is without explanation. What makes a polo shirt more respectful than a t-shirt?

You say there are reasons for the tradition, but you don't say what they are. Traditions may have reasons but they aren't automatically good so it would help the debate to actually know what you thought they were. Note that I didn't say anything to minimize the importance of tradition in general.

Nobody is disputing that people do treat each other differently because of how they dress. The question is, what's behind it?