I tend to look at actions, and the US (in particular the current administration) bears a large part of the blame. The Iranian government is despicable, but so is the one in Saudi Arabia, yet the US has no problem supporting them. The North Korean government is much worse, but the US negotiates with them. Historically, the US has had no qualms associating with authoritarian countries. There's no intrinsic "reason" for the poor relationship, except realpolitik balance of power.