TRT users fall into three camps. Two of which are not good for the sport in my opinion.
1) You're on TRT due to naturally declining testosterone in the body. When you reach your early to mid 30s, your testosterone levels in your body naturally decline. It becomes more difficult for the body to shed fat, gain muscle, and takes longer for you to recover from injury, and/or fatigue of doing a strenuous activity. Athletes such as Dan Henderson use TRT to put their testosterone levels back into the range of someone who is in their mid-late 20s, which I think is unfair. He should not be able to "turn back the clock" with a pill/needle to put himself on equal footing with guys like Jon Jones, Alexander Gustafsson, Anthony Johnson, Phil Davis, etc... He should accept that he is getting older, and his body is in natural decline and find ways to work around that. Change his style in order to compensate for lack of physical ability, or retire.
2) You're on TRT due to steroid abuse in your past and the body has stopped producing testosterone at a normal level and your body's testosterone levels are low due to this. When you take steroids for a long period of time, your body shuts down producing it's own natural testosterone because of an outside source of it being detected in the body and the body will not produce more than needed. When you stop taking steroids, the body needs a "kickstart" to start producing Testosterone again because the testosterone from the steroids has passed through the body, but the body doesn't know that it needs to start producing its own again. I think this is bad for the sport because what athletes like a Vitor Belfort, Mark Coleman, etc... who abused steroids in the past and need TRT because of this, get a leg up on the competition because of their own dubious past.
3) You're on TRT due to a legit medical reasoning like Bigfoot Silva. He has pituitary gland issues and suffers from gigantism. TRT helps regulate testosterone in his body because his body actually produces TOO MUCH on its own, and TRT helps put his testosterone levels into the range of a "normal" person so they will not suffer heath issues in life, and will not need constant surgery on their pituitary gland in order to keep the problem in check. This I have no issue with at all because it is a legit medical reason that deals with a legitimate serious problem.