Before commenting on this situation, I would suggest that you watch the testimony and evidence.
First, Kyle was threatened by Rosenbaum (the convicted sex offender). During the trial it came out that Rosenbaum threatened to kill Rittenhouse and one of his associates previously. “If I get either one of you two alone, I’m going to kill you… I’m going to rip your heart out.” Later, after Rosenbaum chased and hit Kyle over the head, Kyle shot him as Rosenbaum tried to grab his gun. Then, Kyle was chased by a mob of people and ran away. (Not many shooters run away from the crowd.) Kyle ran away to avoid conflict and finally had to defend himself when he was attacked again.
Additionally, because the rifle was not a short-barrel rifle, Kyle could legally carry it at 17 years old and he did not carry it across state lines as parroted by the media.
Now, onto your point regarding Pro-Life.
Pro-Life is about protecting the unborn life of another innocent human being. Pro-Life supporters including most Republicans past and present (Ronald Reagan, Donald Trump, etc) support medically necessary abortions. When the baby puts the mother's life in jeopardy, termination is allowed.
Now, the assailants who attacked Kyle are no babies and they are certainly not innocent, but they put Kyle's life in jeopardy (which was deemed by the jury) and Kyle acted appropriately.