Well, the term has broad and narrow usages. You’re right that the narrow usage (popularized by the Free Software Foundation) only applies to licenses — like the GNU GPL and FDL, or the Creative Commons ShareAlike licenses — that are viral, i.e., which not only free the work itself for redistribution and derivative works, but also require anyone who produces a derivative work to also free it under the same terms.

I don’t have any particular view on what license you ought to use on Libertarian Papers. But I think that the “Attribution-ShareAlike” license would only be “less libertarian” than a plain “Attribution” license if the powers restricted by “ShareAlike” were legitimate powers for an author to exercise. But all ShareAlike requires is that authors distributing a derivative work not try to enforce copyright restrictions with respect to their own derivative work. If enforcing copyright restrictions is illibertarian (as you and I agree), then I reckon that forbidding licensees from enforcing them, isn’t.

Now the new “CCO“, or “No Rights Reserved,” attempt to make one’s work “public domain” seems the most libertarian of all, but its efficacy looks doubtful to me, and it’s still embryonic as far as I can tell.