McHugh entered into psychiatric research with a goal of "ending sex reassignment", according to his own words. He's rather one of a kind in his blatant acknowledgement of his own bias. He's also rather one of a kind in his blatant misrepresentation of other researchers' studies. If it weren't for the fact that he after all is a very skilled academic, I would just conclude that his ability to interpret research is lacking. However, given his education, I can only conclude that he is intellectually dishonest, and misrepresents those studies on purpose.
Sadly, his ability to present his position as if it were founded on science (and the opposing position as if it were not), using half truths and skewed interpretation of research, affects many conservatives, and if you take a detour to certain conservative religious forums (please don't - it'll ruin your day), you'll probably see McHugh mentioned on the first page of any trans-related thread. I don't know how many times I've dissected his statements in such threads, but they just keep coming up. He has done a lot of damage, culturally as well as politically (I've heard that he has been one of the influences behind not covering transgender healthcare through insurance and welfare), and he has even managed to influence the Vatican. If anything, I wish the scientists behind the studies he abuse would be made aware of his misrepresentation, I'm sure they wouldn't like what they see.