It's a professional sport, very competitive and you being able to have a good career and provide for your family depends on whether you can keep winning. I think it's crazy to assume most guys aren't on something, I assume most top fighters are. If you go into a sport full of roidheads, it's pretty arrogant to think you can be champ without taking anything right? People will look for any little advantage they can get.
Most fighters have visibly cheated in one way or another right? Whether it be eye pokes, grabbing the fence, grabbing a glove, grabbing the shorts etc.. DC grabbing the towel to make weight and eye poking Stipe. Kelvin gastelum leaning on his coach to make weight. GSP getting greased up etc..
I think the number of people on gear in pro sports in general is extremely underestimated by a lot of people. There have been times in certain Olympic events where every top athlete tested positive yet now records are still being broken... Natural athletes are beating records set by PED users?? Not likely. USADA makes it harder for guys to be juiced to the gills but fighters can still get away with it they just have to be more careful. It took a bit of adjusting for some fighters.
Also USADA has done shady shit themselves like asking fighters to snitch in order to avoid a longer suspension, giving Mayweather a banned iv etc..