I don't think your take on McCain is correct.
Don't forget his forget his anti-constitutional actions concerning the filibustering of judicial nominees, or his campaign finance reform measures.
McCain / Feingold is an unmittigated disaster in my opinion.
McCain is not my first choice, but I still don't think he's a "liberal" as is claimed here.
In a straight up election between Her Heinous The Wicked Lesbian Witch of the East (HHTWLWE) and McCain it would take me about 1 New York minute to pull the Elephant lever. No, I won't vote for a principaled 3rd party candidate. Best available who can win is my style.
YMMV.