A bad moral argument for abortion

I don't think I will ever understand how people can think it is better to kill children than to have them grow up in difficult circumstances. That's Davidson Loehr's position in a "Moral Argument for Abortion":

We can always breed, but should only do it when we are ready, willing and able to care and provide for our children. While a few kids out of a hundred thousand may make it out of the ghetto, those are unfair odds to pile on a parent, child, or society.

There is an image from September 11, 2001 that was burned into the memory of everyone who saw it: people, sometimes holding hands, jumping to their death from the Twin Towers, with no safety nets to catch them. It should be as heart-rending to see millions of children pushed out into a world that has no adequate safety nets for them either. And to enact laws whose intent is to force the most desperate women to bring babies into a home and a world that can't care for them is, if not evil, a brutality against the most vulnerable women and children in our society -- and profoundly immoral.

So instead of trying to provide safety nets for them, we should kill them faster?

Why don't these advocates of killing unborn children (based on future hardships) ever advocate for killing other human beings whose lives they might consider "nasty, brutish and short"? Where's Loehr's "A Moral Argument for Killing the Homeless" or "A Moral Argument for Killing the Poor"?

If the unborn aren't human beings then you don't need a moral argument for abortion. But if they are then claiming they won't have a quality of life doesn't really have much consistency to it unless you're willing to allow the killing of born humans whose lives you don't consider quality either.