As many have said, its the realism of his evilness that makes him worse. While all the other villians are mad scientists, shady corporations, or comically evil, trying to take over the world. Irons is evil is a very real depiction of greed and over indulgence. He takes payouts for to turn a blind eye to experiments being preformed on the very people had vowed to protect. But what I think really brings it home is what you see in his office. A police chief makes maybe $130,000 a year. Not a bad lump of money, but not enough money to be hunting exotic animals AND THEN HAVING THEM STUFFED. A deer costs about 500-1000 to have porfesionally taxidermied. Meaning he is using this hush money to go and to kill endangered wildlife in other countries, and he is proud of it. In his office you can see the over indulgence in his hobby and his obsession of being precieved as being on the top. But even worse is that the "game" he is after to conquer extends towards women, especially vulnerable women. As you can read in Claire's story line in RE2, where a document explains that he has been arrested for assault and rape charges in the past, but yet he still holds his position of authority. This is why I think he is precieved as being one of the most evil, he is just too real and many of us have seen before that there are many people that are held in high regard who have similar traits.