We can take lawyers, accountants and business people in suits seriously. But we're not on their level?
I guess I'd rather look ridiculous and out of place than look the opposite. If this field is so un-respected, maybe I should make an exit plan anyway.
While I code every day I also part BA. I have a lot of contact with non-technical people - I am not just in a big office with other members of my profession.
Basically if I'm talking to people wearing suits/business casual, and I'm wearing a t-shirts and shorts, they will look down on me. You may decry the arbitrariness of social norms but they do exist and they do effect your interaction in a professional setting, whether people in silicon valley think they should or not.
I want to be respected and I want my field to be respected. If we dress much worse than other professionals, we send the message that we're not really on their level.
Do we? The overall sentiment that I feel in tech (does not mean that I share it) is that these professions owe their prestige to existing power structures and not their own merits or usefulness to society. Developers look down on bankers because it's banker's job to look presentable - and developers think of themselves as actually doing something of essense as opposed to making a show of it.
Other professionals won't appreciate me for my code. A lot of their judgment will rest on my appearance - whether that's fair or not is irrelevant.
Also the implication that we're 'not on their level' due to not wearing a suit is absurd.