Traveling through the depths of time to solve the problems of the past with a vacuum. He has a time machine, and a MD, and he is out to make the future better by improving history. His work has help already, if you thought Hitler was bad, you should of seen what happened with is older bother in charge. You say Hitler didn't have an older bother? Well your right, at least not any more.
The aborted fetuses are not killed, they are kept in suspended animation in case they removal didn't have the desired effect. Sometimes the problem you want to prevent is replaced with a far worse problem. If you have the fetus on hand, you can re-implant the mother and set time back to the way it was. It can be messy, and sometimes the fetuses can get mixed up, that can lead to all kinds of new problems.
If the abortion does change the timeline for the better it is then used for stem cell research.