I agree. I don't think anyone should ever have to 'expand' their tastes if they just damn well don't feel like it. It's a common misconception that settling into a niche is the same as stagnation. The other thing that bugs me is the utter hypocrisy regarding taste. I honestly hate Britney Spears and Christina Aguilera. I can't stand their music, image, and their lack of functioning cerebrums. Yet, they have fans, and as inconceivable as it may be to me, they like that kind of music. True, some of them simply know no better and will gradually break free and discover other styles...but who am I to dictate their taste as inferior to mine or anyone else's if that is what makes them happy.
Caelum Adustum made an excellent point regarding taste evolution by comparing the art listeners and entertainment listeners. In the long run, it truly makes no difference...because those in an artistic mindset who are listening to the music for more than thrills and for a deeper, more spiritual or psychological meaning are perfectly entiled to find that niche and settle in. There will always be a favorite band or song that fully satisfies everything one is looking for. When that is found, the search will stop. It should, anyway. Until then, people can 'evolve' their tastes as much as they want. Just remember that evolution is relative to oneself, and not to others' tastes or desires when subjecting themselves to musical listening, be it for entertainment or an artistic motive.