No Libertarian would claim that Slavery is a State's Rights issue, because the 13th Amendment to the Constitution of the United States of America clearly states:
Section 1. Neither slavery nor involuntary servitude, except as a punishment for crime whereof the party shall have been duly convicted, shall exist within the United States, or any place subject to their jurisdiction.
Section 2. Congress shall have power to enforce this article by appropriate legislation.
Pretty cut-and-dried, wouldn't you say? (Or is this the first time you have ever read the 13th Amendment?)
On the other hand, however, MURDER Law definitely is a State's Rights issue, because no Amendment to the Constitution has ever removed the definition and penalization of Murder from the province of the States Legislatures.
So, what exactly are you disputing?
Well, which is it, Jihadist?
Once a Right to Life Amendment is passed then abortion no longer becomes a States Rights issue, whereas the LP would be out front arguing for a repeal of the 13th since it infringes on the 'rights' of people to abrograte their own unalienable rights.