Given that the vast majority of people are naturally inclined to find it gross and wrong

People are naturally inclined to find it gross and wrong to have sex with anyone they grew up with from a young age, including very close childhood friends but not family members who were largely absent during their childhood (this is very well documented across a range of societies and has analogues in many other species - it's called the Westermarck effect).

So this argument doesn't necessarily apply in all cases. There are broader culture-specific taboos around incest, but they can be pretty weird and arbitrary, e.g. there are societies where it's taboo to have a relationship with a very distant cousin or a sibling-in-law.

I don't really have any strong views about any of this, I just think it's important to be very careful to make sure that your reasoning is sound on this kind of thing, given our long history of banning harmless sexual relationships based on prejudice, then coming up with dubious rationalisations. A lot of the opposition to LGBT rights has been based on claims that LGBT identities are generally rooted in abuse or coercion.

I also wonder how much of an impact anti-incest laws really have on anyone, given that they generally don't seem to be enforced outside situations where there are other crimes going on too.

but when you have extreme differences in power, like that of a guard and a prisoner or a parent and child, then it isn’t safe to assume that just because someone says they consent means that they really do.

But it's difficult to come up with specific rules on exactly how much of a power difference is acceptable, and there are plenty of troubling relationships that are universally legal, e.g. all the Donald and Melania-style relationships between rich old businessmen and much younger and poorer women.