@semck:
Apologies if I misunderstood - but I feel your statement invites the comparison.
Wait, skip all that? Are there not well reasoning and long discussed analyses as to why abortion is not wrong? Now, you don't agree with them, but that doesn't mean it hasn't been hashed out at great length, with well founded arguments on both sides. There are many who believe war is murder, execution is murder, (meat is murder!) and their reasoning is sound, and in no way arbitrary *so long as you understand their moral context* We might not always agree with them, but that's the nature of the beast morality.
Which segues into your second point. I have a somewhat Darwinian take on morality, so yes, I do believe that all moralities are equally valid. They might be abhorrent, but they are valid. Morality is, in a very real sense, the ultimate in arbitrary. Whether your morality is instilled by a higher power, or the teachings of your parents, or your society, how are we to know which morality is superior except that it is the morality that survives?