Lilmod: “Or: Possibility #2: One could argue that someone who votes Meretz is by definition not “shomer Torah u’Mitzvos”.”
Gavra-at-work: “Where is the Aveirah of voting for Meretz? Does this tie into “following the Gedolim”? Wouldn’t that be an additional qualification?”
I think it would be “not following the Gedolim” which is part of being Shomer Torah and Mitzvos.