It's lazy thinking. The whole ethos of casual dress at work was that it didn't matter what you wore, it was about what you did and thought and that we shouldn't make assumptions based on something so superficial.
That's now flipped and become some form of inverted snobbery where the people who objected to being judged on what they were wearing (or not wearing) are now doing exactly the same.
The point isn't that wearing a suit or jeans or whatever is good, bad or indifferent. It's that it doesn't matter.
I've got suits that aren't uncomfortable and weren't incredibly expensive. As for impractical that depends entirely on your life. I certainly wear them less now I have small children but when I was younger I never found it an issue.
In terms of social pressure, well yes, but that's true of a many many things that we do. If you've ever pulled on a clean pair of jeans to go out and meet a friend rather than the dirty (but still hygienic) pair you'd worn the day before, that's social pressure, when you don't just fart in front of people, that's social pressure.
Are those worse than my occasionally wearing a suit to go out with my wife because it makes her happy because she likes the way I look in it? Or because I've just been feeling a bit schlubby lately and fancy looking smart for the day? Or simply fancy a change?
I say this all as someone who typically wears jeans seven days a week and has casual dress as a significant factor when I choose a job.
You say that as if it is an absolute truth. This might be true for you, but it certainly doesn't hold for everyone.
Your argument isn't an argument against suits, it applies to any item of clothing other than the absolutely most basic, utilitarian items. It's an argument against fashion and self expression through clothing of all sorts.
Now if this is what you genuinely believe then that's fine but I hope you're applying the same standards you apply to those wearing suits to people wearing band t-shirts, anything branded where an equivalent non-branded item is available, or frankly anything that has been chosen for any reason at all other than it's absolute functional value.
Or my other clothes were in the wash. Happy now?
Is that not a clear enough example of why your argument isn't just about suits when I can just reuse your answer an it works?
In this sense it's a far better reason for a suit than for a band t-shirt. A suit is the primary output of a tailor, a band t-shirt is a commercial by-product of a band. There are better ways to support a band than buying a t-shirt - buying their records or seeing them live for instance. There is no better way to support a tailor.
As for the circular reasoning on its dirty - I agree but it's the same for both suit and band t-shirt. You have to have a reason to own it which I've given you.
Regardless of that owning and wearing a suit because I think it is a beautiful example of clothes design, regardless of whether it supports the creator or not, is a valid thing to do in itself that is neither narcissistic nor an example of social pressure.
And in case you think I'm desperately trying to come up with reasons but that they're not actually things any real person would do, I own only two suits, one of which (by Oswald Boateng) I own precisely for this reason - because I believe it to be a beautiful item (or more precisely two beautiful items) of clothing.
But the problem is still that your argument applies to lost of clothes, not just suits. Shirts are less practical than t-shirts. Buttons are fiddly and unnecessary, collars a pointless throw back to necktie and don't get me started on the practicality of cuffs. Most shoes are sub-optimal from a pure practicality point of view. Ironically many trainers aren't actually good for running because of the way they're balanced.