What people choose to associate themselves with in public is exactly fuck all of your business. Don't be like the meme guy, tend to your own garden.

Gatekeeping really is not either of these things, but people can wear whatever they like. I can't say I get why someone would do it at all, but not my problem.

There's a huge difference between using it as a conversation starter and asking about their favorite songs or whatever, since it's reasonable to assume they know and like the band, and going "name 3 songs" because you assume they don't listen to the band and also somehow care about that.

Gatekeeping isn't inherently misogynistic or conformist, but the motivations in cases like this probably are.

I also don't think it's unreasonable to ask people not to publicly associate themselves with a thing if they know nothing at all about that thing.

Nobody owes anyone an explanation of how entitled they are to wear a band's t-shirt.

I've listened to enough iron maiden to know that I like the band, but could only name one song off the top of my head. Do I have your permission to wear their t-shirt?

You're channeling the same energy as someone that feels entitled to know about a stranger's genitals if their bone structure seems misaligned with the gender they're presenting.

It's so easy to not be an asshole watch this:

Slayer fan:

Iron maiden! Nice! I saw them play at XXXX back in XXXX. It was a wicked show.

Iron maiden fan:

Oh wow, that sounds so fun! I've just learned about them, but I'd love to see them in concert someday. The metal community is so welcoming!

Or:

Oh wow. I don't really listen to them, but they were my cousin's favorite band, she died recently, so I wear this shirt when I'm missing her.

Or:

Oh wow, I was at that show too!

Or:

my uncle is the drummer and is always giving me these

Or:

Uh huh? I just like the colours of the shirt.

Life is so much better if you don't make nasty assumptions.