Libertarianism is founded in the principle that the human being is free.
FREEDOM. Not "right to life." and Not "non violence" -> the founding principle is FREEDOM. Liberty. Libertarian.
And so long as a fetus is created and develops within ANY HUMAN -> that human has complete authority over the situation.
Religious Arguments? Your religion doesn't give you the authority to INVADE MY BODY.
Any other argument? I am free. As long as it's in me - it's MINE.
You want to let the government start REGULATING ACTIVITIES WITHIN THE HUMAN BODY?
Are you insane?
No. You're a Libertarian. You understand freedom.
And if people ARE committing some atrocious act - leave it to GOD.
The benefit of the doubt goes to.... FREEDOM!