Some people just squick out over stuff they don't understand or aren't attracted to personally.

Some people... If you're raised to think a certain way, to believe a certain way, it gets ingrained pretty deep in your thinking. Especially in cases of people with very insular social groups, or people who were raised in a somewhat restrictive environment. And if you have both been fed misinformation, and told your whole life that God is against something, then you have an incentive not to seek out facts that say otherwise - you don't want to anger your god, do you? It can be quite difficult to counteract that, even for people who are in the closet themselves and have every reason to fight back against beliefs that would lead to their self-hatred. Some people stay with the party line, some people listen to a different way of interpreting religious texts to give themselves freedom to learn, and some people don't feel safe acknowledging that what they were taught was wrong on some points until they've made a clean break from their early religious tradition altogether. For folks raised in the deep end of Christian "Conservative" tradition, if they change their mind it often seems to be either because they've started seeing a different point of view on religious beliefs - or because they have had enough friends come out to them, that they can't picture in their heads anymore how a God worth serving would be cruel enough to reject people on that basis.

As for Sekah's discussion of the Biblical scraps used to justify that viewpoint - when it comes to Leviticus there is a running debate in some Christian circles as to what parts of "Old Testament Law" were valid only for those who received it at that time, and what parts are applied to everyone following God today. The debate is phrased in terms of "moral" vs. "ceremonial" rules, and something is more likely to be considered "moral law" or still valid if whatever theologian arguing about it can find support for the same rule in the New Testament. And when it comes to Paul - a lot of folks would argue that he DID know Jesus, in the sense that he met him in a vision when he first converted and there are a couple passages folks argue MIGHT point to him claiming to have had follow-up visions since then? Also, there's the question of whether his contemporaries, Jesus' actual disciples, would've had the influence to shoot down anything he said that directly contradicted their master's teachings. The justifications can get pretty weird, but it is slightly more complicated than just these passages are irrelevant why are people still arguing - especially when you factor in people's fear of hellfire and damnation should they make The Wrong Choice in how they interpret things.

^in my experience, not sure about range of applicability