Monkeys also engage in cannibalism, sometimes even of their own dead young, and lions regularly commit infanticide. Appeals to nature are not compelling in the slightest when it comes to morality.
As for my moral argument, I invite you to read about the history of abortion, the history of abolition, and/or the history of America's war on drugs. I expect you will find abolition the easiest example to grok, since it's no longer a political issue. Note the moral arguments for abolition still stand, and yet it's no longer law.