My thinking...Exposure. Some type of standard about what is good based on the sound or idea. That automatically means another style is "bad" based on those standards.
I think most peoples musical tasetes are acquired by the time they are 17-20 yrs old. I still listen to many of the same things I did at that time in my life. I just listen DIFFERENTLY than I did before. Exposure is key I think too...
Sometimes I'm thinking, This is "great" music because I've been told it's great.