For metal and the like, it's about theater. Most in that genre are real pussycats, they're just having fun and they don't take themselves very seriously, like Alice Cooper. He'll make a deal like Faust and then get his head chopped off one night, and the next day he's laughing about it at a charity golf tournament. Metal itself is an acquired taste and I was raised on it, lots of Black Sabbath and Led Zep, at 10 I could even sing all the AC/DC Bon Scott songs by heart. I was inconsolable after he OD'd. So, my tastes are impacted by cultural influence, like anyone else. Never did get into the harder stuff, though, like Cannibal Corpse or Deicide.
For me, I believe it comes down to a couple factors: is the singer(s) actually singing, or are they only talking, growling, or screaming? Is there coherent melody, or an artistry at work that I appreciate on an emotional or technical level?
Rap/Hip-hop lovers shouldn't feel bad, though, I feel the same negative response when I hear Pop-Country, so it isn't exclusive to one genre.
I used to spend quite a bit of time in the metal scene, particularly the death metal scene in Denver. (I got into it because I used to record some bands in that genre.) The people are generally pretty laid back and fun, though they are often the "I'm super nice unless you trifle with me" type. They are generally not the type of people you want to directly screw with, and they will make a point to prove that's not a good idea. There is also a definite etiquette to the culture.
As you said, Metal is an acquired taste, and one that IMO often starts young, when music is a source of energy, motivation, and sometimes aggression. I also think that people acquire different tastes in frequency balance and tone; Metal has a particular feel in that area, along with the concept of "distortion can be beautiful".
I like some rap, but probably only 1% of what I've heard. I also tend to have an aversion to country. The odd thing about that is that I was on a light crew for 15 summers at a country focused venue. So I've seen most of the major country artists, but never acquired a taste for their music. It does have its fine points, such as a certain amount of emotional depth, especially in the area of loyalty to one's spouse and family. There are also some very talented musicians in that genre. Seeing Charlie Daniels play fiddle breaks any urge to mock the talent level. But the genre overall is pretty simple structurally, generally being in 4/4 time with a 2/2 backbeat, and usually in a key of C or D. Other genres such as Metal, Classical, and Techno are worlds more complex musically than country is, and I enjoy that diversity. 
EDIT: Typing this post reminded me: Willie Nelson has a bright yellow Neve console that he takes on tours, which makes him cooler than anybody. Most bands don't have the balls or the budget to tote around a $100,000 sound board, nor do they have the style to have it custom built in bright yellow. 
Edited by barleyguy - 10/9/12 at 9:33pm
