Agree to an extent, but also understand that these guys are not doctors. They're athletes. While I agree that they are accountable, at some point nutrition and sports medicine becomes voodoo and witchcraft for all these athletes know about the stuff. They are told by people they trust to take this, eat that, jump this, lift that. In a sport where the slightest physical edge can be the difference, I don't know that it's possible to fully know or understand what you're ingesting all the time.
True they are not doctors, dieticians, etc. but in the end they jeopardize their career by just ingesting anything. These athletes need to be smart. Having worked and lived around Collegiate and Professional athletes and being an athlete myself I totally understand the affects of friends, trainers, etc. saying take this as well as the athletes mindset of wanting to take, do just about anything to get an edge. The allure of anything that will give you an edge is almost unstoppable when large sums of money become involved and also when you age. Yet, professional athletes around the world have to work within their sports rules and understand them so that they can compete. If they screw it up in mma they won't be working and making any money so the onus is on them to really be smart about this!