I personally detest the modern scientific thought-frame that its just "a clump of cells". That terminology seems Orwellian to me, and is a slippery slope to quickly dehumanize the subject.
I'm in favor of a choice to abort in special circumstances such as rape or mental defects, but then again that simply opens the door to more loosely defined slopes. Its like...where do we draw the line? Its either 100% yes or 100% no.
My stance is, early term okay, I don't agree with it so I won't participate with it. However I don't think its my right to make that choice for other people, however once the fetus can survive outside the womb(which is earlier than most seem to think) then absolutely not. Period, its no different than murder at that point.