This is me on web design.
However, I don’t think grammar or clothing or web design are “deeply arbitrary”? Some sentences are less ambiguous and comprehensible to a wider range of listeners and shorter than others. Some garments are better at protecting the body without overheating it. Some web pages match the official definitions of elements better, and are more compatible with a variety of browsers (screen-readers included).
I’m basically one of these “same people”. I see fashion as a language, and I judge people for what they say in what context and how they say it. And the same for graphic design, and for architecture, and so on.
Is there any way for me to opt out of this? Mandatory beauty labor is always and everywhere obnoxious as fuck.
(Okay I realize I automatically get to partially opt out by being a dude, but)
Opting out <i>as such</i> is hard. However, there’s my usual dress sense – I like to describe it as the intersection of “plain”, “conformist” and “low maintenance” but I’ve suddenly realised that “clean” (hah! – Ed.) and “in compliance with the not particularly arduous work dress code” are also a part of it. The message is “This page intentionally left blank” or “nothing to see here, move along”, past experience at school has taught me that any message you send <i>will</i> be misinterpreted, often wilfully, and “blank” is often safest; fortunately my school had a school uniform so I was spared one aspect of that.
The trouble with all of this is it all gets terribly depressing after a while…
My current frustration is trying find something to function as a purse that’s socially acceptable as a man. Since high school I’ve used a drawstring bag* but this seems like it’s both not terribly professional and getting less acceptable as I get older. But I still need something to carry my epi pen + wallet + checkbook + phone + keys + ideally hand sanitizer + anything else I need to hold on to. My alternate strategy is cargo shorts, which run into a similar problem. I’m sorta confused about how other men manage this. And in regards to the OP, I do think of this as “deeply arbitrary.”
Like one of these: https://goo.gl/images/JJbw25
You can get some fairly professional-looking laptop bags, and they hold a lot, even if you put a laptop in. My Consultant Bag (Note block, pen, post-it notes (you’d be surprised how often those come in handy) toothbrush+paste, laptop, power supply) is a 15 inch laptop clamshell bag  from Targus, and absolutely nobody bats an eye at it because of course a profesionally-dressed man can carry around a laptop.
EDIT: And in my daily life, it doesn’t actually hold a laptop, it’s just a bag that looks like it holds a laptop. It did in my old job, but not any more.