Edit: Some people struggle with simple pronoun usage and understanding, so the OP is edited for those with such "reading impediment".
I know incest with the aim of reproduction can cause some nasty genetic permutations on a lineage but aside from the aim of reproduction. How do atheists or the irreligious perceive incest with the aim of pleasure or fun since atheists obviously don’t get their morals from the bible?
That is something you would have to go around asking each individual atheist. There is no overall “atheist mindset” on subjects like this. There are those who may be fine with it and practice it themselves. There are those who might find the practice disgusting. Then there are those who don’t care one way or the other. None of their business what two (or more) consenting ADULTS do behind closed doors. Then there are all the variations in between. Basically, it is misleading and incorrect to ask what an “atheist stance” is on that matter. Might want to be mindful of that for future reference.
As for my personal view on it, I’m one of those who does not care one way or the other. None of my business if some dude likes banging his mommy, or if sister and brother have a roll in the hay now and then. To each his/her own.
If it makes you feel any better, I’m pretty sure Old Man was not talking about you specifically. And I am most certain he fully understood the OP. In that particular case when he said, “…if you wish to have a CONSENSUAL sexual relationship with a relative…”, he was speaking in general terms. Rather like if somebody asked me, “How do feel about people fucking chickens?” My reply would probably be something like, “Hey, man, if you want to stick your cock in a cock, it ain’t none of my business, and I don’t want to know.” See?
I find incest to be repulsive and pathological . . . but so is smoking.
This animus against incest seems to be ingrained in our genes, as children (for example) who grow up together in a commune (like an Israeli Kibbutz) almost never marry each other, even though they are unrelated. It’s “gross” because they’re family.
And then there is the opposite phenomena, called genetic sexual attraction, or GSA.
It seems that blood relatives seperated at birth–when reunited in adulthood–often experience an instant, overwhelming sexual desire for each other.
An interesting side note to this thread is a couple from England who met, fell in love, and got married.
After several years of marriage, they found out that–by coincidence–that they were half siblings, as they were both conceived in vitro from the same sperm donor, as their parents had fertility problems.
Their case is being appealed to the British equivalent of the supreme court, as British law demands that their marriage be annulled . . .and that they would break the law by remaining together.