As many have said, maybe not with parental incest relationships since, as many have said, there is a power struggle going on in the middle of the relationship. The child was probably even raised to see their parent that way and no matter how it looks on the paper/roleplay site, it is far more suspicious in real life.
So, a parent could have raised their child in a way the child wants and desires the parent in a more romantic way, but all of it is just indoctrination by the parent. If you are dependant on someone, even after being legally able to give consent, you have probably been raised to still depend on your parent in this scenario. How do you say no when food, shelter and commodities depend on accepting having a thing with mom or dad? It is something it'd have to be looked up into. Also, how do you exactly break up with your parents after that? There is no guarantee that the parent won't turn manipulative, wether by cutting off food, making you pay rent, using physical or psychological violence or downright guilt tripping you with all the things they did as a parent for you or how they would never find someone else. So, that's a huge power struggle. I think if parental incest was legal, single parents would use it to make their children stay in the nest. We have single parents raising their child so they depend always on them, so I don't think anything would improve if parents have the option to get in a relationship with their offspring.
As for fraternal incest or someone else that is not directly linked to the family (cousins) I really see no problem. Of course, both parties should be consenting while also having a reasonable age difference. A sibling or a cousin 5 years older, while still being a minor, could convince the younger party that their relationship should be. When looked in closely, one party had convinced the other. I am pretty sure there are laws concerning that matter so I won't get much into that.
My opinion doesn't differ from most of the ones I have seen, yes, incest should be legal but...
Both parties have to be in the consenting age, or meet the respective law standard when the two are minors. But I would prefer if incest was only allowed when the two are consenting adults.
Only between siblings or cousins, parents will most likely twist their children like puppets
While legal, it is still something to look up into.
I don't think it should be illegal, but it should have its limitations. As long as both parts know what they are doing and don't harm each other, that's fine.
Also, if we are going the "extreme" route. If I am allowed to go down that way. Parties of incestual relationships should either use obligatory means of contraception and should not be allowed to have children.