If 50%+ of miners decide to do something, and they have the programming ability, they can make bitcoin into whatever they want.
You mean if miners (mining pools actually) that control >50% of the hashing power decide (i.e. nothing to do with the % of miners as you could have 90% of miners only controlling say 30% of the total hashing power).
Such ideas of "black lists" have been brought up many times before and thankfully they haven't been adopted. If they do get adopted then Bitcoin would have a very big problem with regards to "fungibility".