I'm not sure what kind of opinion you were looking for, but
I think it's stupid. You like a song, but when someone else likes it you treat it like it's cancer. wtf? What was the point of liking it in the first place? Personally, I don't really care if it's mainstream or not. But since mainstream music gets more attention, it's bound to attract a huge amount of people everywhere, including people who don't like that particular type of music. Being mainstream doesn't necessarily means that it's good, but in most cases, it's successful. Popularity = Success.
Even that rebecca black...thing gets a second song. A SECOND SONG YOOOOOOOOOOOOOOOOOOOOO! Then, I noticed some people "changed" their opinion about her and suddenly liked her because liking her was the "not mainstream" thing to do. They were looking for a reason to do that all along and they found it because her second song didn't SUCK as much as her first one. Liking a song DOESN'T depend on how many people know about it or not. It's how many people that like or hate it. Or just people that want to fit in with/rebel against society.
tl;dr: i think so