Joe Rogan made a good point on the last fight companion podcast. It isn't necessarily the opinions of fighters, but the opinions of sponsors, litigators and the general public that are important in considering whether to test for PEDS. These people already see the sport as fairly barbaric, filled with tattooed criminals and just generally low brow, rightly or wrongly, and if you then throw in that they are cheating PED abusers who are, in their eyes, beating each other into a pulp, then the sport suffers.
It suffers because it can't attract sponsors, it gets less exposure, so less people take it up, has trouble getting certain laws passed and any number of knock on effects that you can't even guess at. If the sport wants to legitimize in the eyes of the general public, then it can't be perceived to be roided out cheats indulging in gratuitous violence.