You're absolutely right. So instead we'll celebrate the fact that there will be fewer babies killed now as a result of what happened.
I’m celebrating that the planet has one less mass murderer. We have a new murderer, but at least he’s apparently in custody. Sounds like a net gain for good.
Do you think, seriously, that killing George Tiller is going to stop further abortions taking place? Because if you do, you are going to be sadly disappointed. He was an instrument of abortion, not its cause. The social and moral conditions that enable abortion existed while he was alive and they still exist now. All that will happen is that someone else will do the abortions at that clinic now, and you can transfer all your moral disgust to them if you like.
Abortion on-demand happens because the technology exists to do it, and the personal moral integrity that says “I didn’t plan this child, but now its happened I cannot selfishly destroy a Human life for my own convenience” hasn’t caught up with it. The way to close abortion clinics is to make them obsolete by presenting the pro-life argument so irrefutably that no one wants to use them.