In other words, abortion is done out of compassion for the one being ripped to shreds.  Using this perverted logic, slavery could also be rationalized.  From a purely utilitarian standpoint, it could be argued that a person is better off as a well-cared-for slave in America, than slowly starving to death in some filthy AIDS-infested third-world dictatorship.  

Also, how do we identify which unborn children will lead these terrible lives so we don’t inadvertently butcher some who might have lived good lives?  Should only women who promise to give their children terrible lives be allowed to have them killed?

We also know that a lot of born children already live terrible lives.  So why don’t we start killing them as well?  After all, if it is compassionate to kill people who might live a terrible life someday in the future, surely it is even more compassionate to kill people who we know are living terrible lives right now.