To Preface this, some questions should be answered:
1) Is being alternative a choice, or fashion style that can be easily removed like a costume?
2) Who sets the standard of acceptable dress codes?
1) I do not believe it's as much of a choice as most people would say it is. I believe there's underlying psychological factors that make a person attracted to things outside of 'the norm;' especially things of a morbid nature. Alternative people seem to have less of a fear/disgust response than most people. There also have been links by psychologists, between tattoos, piercings, body scarification, and sexual orientation:
https://www.encyclopedia.com/social-sciences/encyclopedias-almanacs-transcripts-and-maps/piercings-tattoos-and-scars
2) Where do "the rules" regarding what is 'acceptable' or 'normal' stem from? Those are socially mores based on religion, and gender roles. It's the same reason why men are told in the work force that they cannot wear eyeliner and women are expected to not shave their heads. If there wasn't such an influence by Judaeo-Christian theocracy, many of these 'norms' would be non-existent.
So, with that being said, society is the way it is. Is there a way to circumvent being able to maintain self-expression while having a stable career? Thankfully, like everything, we live in a world full of nuance.
With pop culture adopting many alternative styles such as unnatural hair color, tattoos, this is becoming blasè.
What is a reasonable dresscode? Is allowing someone to stroll into a bank teller position whilst looking like Tank Girl reasonable? Not in today's current society. Is allowing clean, unnatural, say purple, dyed hair, with glasses, a suit and tie? That is becoming more of the future, and is already happening in major cities.
Starbucks already allows employees to have any hair color as long as it's kept well, and a nose stud.
***The Discrimination Factor***
What do I mean when I say alternative people are discriminated against? I would even argue that alternative people are discriminated against more than many other marginalized groups of people.
1. They are seen as subversive against religion (which is many a times the case, and thank goodness for that, let religion die!). Because they deviate from traditional gender roles, and in the case of piercings (depending on where), are open displays of being proud of being kinky.
2. Old fashioned notions of rock n roll and drugs. The baby boomers grew up in a time where 'hard rock' meant shooting up heroin and waking up the next morning with 10 STDs. Unfortunately, this stereotype gets passed on down to today's alternative youth. Despite many straight edge movements, and some subcultures that encourage academia, the stigma will need another generation to die off to be free from.
3. Homophobia. Take the Gothic Subculture, for instance. It's a subculture where often, at least in the better scenes (especially Germany), men wear makeup, have long hair, are in touch with their feminine/androgynous side, whilst being completely heterosexual. Men are always treated more unfairly in that regard (see: women being tomboys being seen in some cases as endearing).
4. Simple fear/disgust due to beauty standards. Hollywood culture tells society that it's socially acceptable to dowse one's self with spray on tan, more botox to pollute the Pacific Ocean, wear baggy jeans that fall so low that a person's vertical smile gives everyone a friendly 'hello,' or in the South, to have a 20 missing teeth, have rugged leathery skin due to being 'fuck it' about taking one's health in consideration. In today's society, it's more socially acceptable to be trailer park trash or looking like a Springer Show guest than to actually be a Goth, Metalhead, Punk, et cetera. Because the alternative subcultures are subversive, and terrify those with a high fear/disgust response.
**Last take**
No one really mentions it, but even groups that are deemed marginalized, have a hatred toward alternative styles. Turn on any mainstream show focused around style/beauty. It isn't uncommon to see a flamboyant, gay, man, critiquing and mocking someone for having an alternative style. He'll shriek and make some reference to a 1980's musician that doesn't even make sense (see: calling a Goth woman 'Cyndi Lauper).
Sometimes POC communities are super intertwined with conservative, religious, values. I've known several people who grew up in South Central Los Angeles, who were attacked for how they look, by people that also deal with being attacked for their ethnicity (make it make sense. you can't).