First of all if some fetuses die or are "aborted" by natural causes how would hurt anyone to use these cells in medical research? They fetus is already dead, so who is it hurting, except the 4 year old who is dying of terminal that could be cured by research, but is going to die instead so you can stick to your illogical principal. Bravo.
Also ultimately it doesn't matter, if you or I or anyone else here likes or dislikes abortion, its not going to become illegal anytime soon. Personally I think abortion is far too much of a messy subject, so frankly I have no real opinion on it. However I am a pratical individual, pratically speaking since abortions are happening anyway, whether you like or not, why not use cells from the festuses in medical research? They are going to get aborted either way, so what's the harm in using these aborted festuses' cells to promote medical research that could save the lives of many people in the future?