1) Entirely subjective
2) If I like or dislike something it only means it is good/bad to me, not as an universal truth or fact.
3) There is no good or bad taste, but I think the more interested you are in music, the more open you are and the broader is your taste in general. People who are raised on a diet of radio and MTV define what they like by what is generally and socially accepted as "good". It is a question of fitting in. Nobody wants to be excluded from the group. So if you want to be "cool", you just HAVE to like certain things, you know..