Reign: I guess they're just worried about your safety because these types of concerts do get a little bit rowdy, in terms of people constantly moshing and whatnot. I've been to concerts like Bazooka Rocks and you might be surprised that not all people are only looking after themselves. Some do help you out in case you get hurt, but the chances of you actually being unsafe during these shows are extremely low (based from my experience). Plus, there are always security guards/bouncers and medics around. You can tell your parents about what I said, like how it's pretty safe and stuff. If that doesn't work out, try to bring your parents to a show you want to go to so they'll feel that you're being looked after haha.
Marian: Try asking for help from your friends who have been to these types of concerts! Ask them to kindly explain to your parents how safe it can actually be. These concerts can actually be pretty tame if you know where to stay (not in the middle of the crowd) and mosh pits are not really allowed anymore in most concerts. When you convince them, try to bring someone with you whom they completely trust, like a friend, a sibling, or a cousin, because that can greatly help ease their mind when they know that you are with someone they know can keep you safe.
"My mom won't stop pestering me about my fashion choices. She wants me to wear something other than my jeans and shirts and shorts because she thinks what I wear is a reflection of my sexuality... and let's just say she's not one of the most open minded people out there... How do I explain to her that your clothing choices do not indicate your sexuality??"
Reign: I think you have to tell her just exactly what you think about the situation; that your clothes do not define you as a person. One way of convincing something to someone is by educating that person and I think if you show her that clothes are just material things made to cover your body and not who you are up, then (hopefully) she realizes that. I guess what she wants is for you to look presentable to people, but then your fashion choices are for you and not for others. Don't stop dressing they way you want to.
Marian: Just like what Reign said, one way you can really convince someone of something is by educating that person. Try to initiate a nice, formal talk with your mom and kindly explain to her that the way a person dresses up is not a reflection of who they are as a person. You wear the clothes you wear because you like them and you're comfortable with them and when your mom reprimands you or something, in a very nice way, tell her that you're the one wearing the clothes, not her. Don't let that affect how you dress, continue dressing for yourself.