LuL – I don’t believe Meretz would be against your definition of Chareidi, if they could support themselves, be in the army (as someone living in the country, not a Zionist (they would do the same as if they lived in Canada)) and the peace process. Meretz (or Lapid) would not exist to oppose Ner Yisroel graduates who went to college (who by your current definition are “Chareidi”).
It is more of the deep sociological divide between those who vote Gimmel and others in Israel that Meretz (or Lapid, etc.) are against. Chareidim (as per your definition) can be on either side of that division.
Or: Possibility #2: One could argue that someone who votes Meretz is by definition not “shomer Torah u’Mitzvos”.
Where is the Aveirah of voting for Meretz? Does this tie into “following the Gedolim”? Wouldn’t that be an additional qualification?
Possibility #3 is saying that the definition of Chareidi can vary? Not much of a definition then.
Since #1 seems to be correct, would you mind please describing the extra qualifications that you are adding?