can we for the sake of diversity allow 1 Billion migrants from Africa and the ME in the USA?

That is not where the majority of immigrants to the US come from and of course this country can't even support its current population let alone another billion people (no matter where they come from).

We could, but only if we also allow in enough migrants from Latin America to produce enough food so that we can feed the other migrants. We actually have enough farmland to feed the entire world; we just don't have the workers.

The environment would improve, because a person kept out of the U.S. is worse for the environment than a person allowed into the U.S.

I'm glad I live on the cliff over the Yellow River where mu three hole outhouse flows down to the river below which flows to the little hamlet downstream where the peasants wash their clothes in the mornings.

Oh, the Democrats would love that. What could be better than a billion uneducated, emotionally unstable people from poisonous cultures to be "sheeple" for the Left?

That is an exaggeration. However some statistics reveal that upwards of 150 million people worldwide want to come to the US. I don't think Liberals have thought through how much damage it will do to establish a whole new class of unskilled, uneducated, ignorant dependents.