I've been reading Natural Rights and the Right to Choose by Hadley Arkes and he points to an old argument by Abraham Lincoln used to discuss slavery that I've heard paraphrased and I thought I'd post it here.
You say A. is white, and B. is black. It is color, then: the lighter having the right to enslave the darker? Take care. By this rule, you are to be slave to the first man you meet, with a fairer skin than your own.
You do not mean color exactly? - You mean the whites are intellectually the superiors of the blacks, and therefore have the right to enslave them? Take care again. By this rule, you are to be slave to the first man you meet, with an intellect superior to your own.
But, say you, it is a question of interest; and, if you can make it your interest, you have the right to enslave another. Very well. And if can make it his interest, he has the right to enslave you.
Which arguments in favor of abortion fit this mold? Size, dependence on others, location, degree of development, and brain function are a few I could think of.
Which arguments for killing Terri Schiavo by starving/dehydrating her to death fit this mold?