Alright, music snob here. Here's my point of view on the whole 'mainstream' debate thing.
Its not so much that I hate a band because their mainstream (well, lets face it, what I listen to is pretty freakin' far). It's the fact that 99% of the mainstream music out there is generic, made-for-the-masses, auto-tune garbage. And that is the ONLY type of music that is getting exposure to the people, and thus, what they are forced to like. I mean, unless you know someone who tells you to check out some other ways to get exposed to more underground stuff, your just gonna sit with what good momma radio gives you.
And about #1's, Whoa, closed-minded much? I mean, yeah, I'm a metalhead, thats because every other kind of music I've heard of besides Classical (which I like too) lacks the progression and emotion to keep me entertained.
About #2's, Well, read the first big paragraph.
About #3's: The whole 'sellout' thing is controversial. I'm PERFECTLY fine with a band getting famous on their own talent. However, let's take an example I know about, Metallica. Alright, so during the 80's Metallica were one of the best bands metal had to offer. However, when they went into the 90's, they decided to change their sound SO MUCH that it completely alienated a large amount of their original fanbase and such. Then, they realized that, despite they weren't truely the original Metallica, that new sound that came in 1991 with The Black Album would make them more money so they stuck with that particular sound. That is one of the reasons I don't respect them, they sold out, as in, changed their sound for the SOLE purpose of making more money.
Now let's take another example that I know of, a more obscure New York based Metalcore act, called Through the Flood. At this time, they have recently released their very first EP. I absolutely adore their music that they have created so far. Anyway, they are trying to get signed to a record label called Victory Records, that produces a lot of other Metalcore and Deathcore acts, such as A Day to Remember, Carnifex, Aiden, and Between the Buried and Me. If they got signed and started making money, that would NOT at ALL be selling out, for they didn't change their sound for the sole purpose of making more money, instead, they would get signed because their music is good.
Well, yeah, there be my opinions, feel free to agree or disagree.
EDIT: Whoa, I just realized how well my new signature seems to fit the 'selling out' topic.