Mma is evolving. We found out how bad hard sparring is. A few generations of fighters ago, we had guys like bas advocating hard sparring twice a week. Chute box wars. Etc
Fighters are going for longevity, because when it's our brains and bodies on the line, that should be the priority.
Guys like Frankie Edgar are ahead of the curve. Weight cutting severely fucks with the brain and hormones. Now he's cutting weight, and still in a heathy range.
Just like fighters are figuring out hard sparring isn't necessary and in fact detrimental, the same will happen for weight cutting. Longevity over temporary advantage.
I believe the same will happen for PEDs. Fighters will realize the cons outweigh the pros 
While I can see that weight-cutting cons outweigh the pros, I doubt we'll see the same thing with PED's, so long as people are able to develop PED's that are different enough to not show up on the tests.
Sports that have been around for much longer have been battling the same thing (with varying degrees of conviction), but the one constant seems to be that the people making the PED's worth using always find a way to alter them so as not to show up on a drug test.
Sure, you have to have money, hence the term "designed drugs", but those Performance Enhancing Drugs still exist. 
The truth is that the cons for peds are not what people think they are because of government propaganda. In fact they're extremely mild if you don't go full retard with them.
The biggest con is the risk of getting caught