It's such a paradox, that someone who is pro-life should attempt to kill another to achieve their "pro-life" ends...
Although there is some logical appeal to the argument that killing is justified during war, and in this case, the thousands of abortions each day constitute a war on the unborn... ultimately I think this notion has to be rejected, since the 'battle' isn't so blatant as to be fought on any declared battlefield with any declared enemy. As corny and stupid as the term sounds, it's more of a 'spiritual battle' that needs to be prayed for, actions taken within the system to decrease and eliminate either 1.) the need for thousands of abortions each day (ie - giving mothers a respect for their unborn fetus, providing them aid during and after pregnancies, etc) 2.) end the legal option that parents possess today to abort their unborn.
As it is, bombings and loud, yelling protest have very distasteful (to understate it quite a bit) and, dare I say negative, outcome regarding changing hearts and minds of the large portion of the public that aren't firmly for or against abortion rights.