I am an atheist and consider The Law of One plausible

[anagogy]

I have an atheist friend who is somewhat convincing. He says how can there be reincarnation if Earth's population keeps increasing?

I always laugh when I hear people use this as an argument.

There are more individuated souls in in the spirit world in queue to incarnate than they could possibly imagine. And they also aren't limited to incarnating in one time reference, and there are parallel realities as well. Of course, a materialist isn't equipped to understand that in the first place, and will inevitably see such an argument as some kind of cop out.