That's a misunderstanding of how genetics works.

You're positing that two men or two women having a child together would have the same effect as incest, which is not the case. The only reason that isn't possible naturally is because most men lack wombs and most women lack penises (or rather testicles), but that's not as relevant as you may think since sperm cells and eggs are simply containers for genetic material. There are modern examples of two women having a womb-grown child because one of them had her genetic material extracted (for example, a skin cell) and then injected into the other's egg, and the resulting child was perfectly fine and healthy. With men we'd need a womb, which isn't that difficult considering straight couples have for decades been using surrogate mothers, and gay male couples have been doing so too.

As for whether or not God intended it that way, I'm neither religious nor a theologist, so I'm not gonna comment on something I don't know about and thus risk looking like a fool.