It's their fault. These are grown men and women, adults that should take full responsibility for their actions. If they choose to take performance enhancing drugs to give themselves an unfair advantage over their opponents then they should be punished appropriately. And in my opinion, a permanent ban is appropriate.
If the UFC want to cut down on the number of steroid users in the sport, then they should look to make an example out a high profile fighter. If any one gets caught using PED's then they should be banished from the sport or the organisation. I'm sure that would make fighters think twice about ever using them.
At the end of the day this is mixed martial arts, the best fighter should win the competition. Using PED's to gain unfair advantages goes against everything I watch this and other sports for. Everyone should be on an even playing field.
I don't really disagree with this, and I think they could do this going forward. If they announce now that the next person that gets caught is fired, and will be permanently banned from Zuffa, then ok. Everyone has been warned and if they are caught it's on them.