The argument against incarnation is pretty clear. Let’s say you believe in some ultimate reality — a transcendental source of creation, being of all beings and perfection of all perfections. How could that being be a particular person? How could it be born, die, go to the bathroom? What does that even mean?
An argument for incarnation is that if we think about such a Being of All beings, it is already incarnating in us, as we are thinking that thought. And we are born, die, and go to the bathroom.
So, everybody believes in incarnation. The only questions that are left (and they’re important) are how, why, and who? For a long time the last question was answered “my guy (or lady) and definitely not yours.” But now that the human race has invented WMD that answer is too dangerous for anybody of good will to maintain seriously. It’s also, once you get to know something about how these ideas pop up all over the place, pretty unsupportable.