In my personal opinion, the zygote created in the fertilization is a unique human genome, DNA and all. In my opinion, this is more then just potential human life, but it is human life, albeit living through it's mother.
Case in point, When I worked as a EMT, I'd often get called to check on homless people living under bridges. Now, I offered them assistance, becuase they were human beings. I'd clean their cuts, bandge them up, etc, etc. With the same line of reasoning given by Peaceuponnus, I could have said, " These bums don't contribute anything. Why waste my skills and materials helping people who won't help themselves! They'll just continue being poor. "