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Firstly, it's not even a simple slam-dunk case that Bergoglio is a heretic.  If there's one thing I could get him on, it would be his rejection of EENS.  Yet, ironically, most SV Traditional Catholics hold essentially the same position on EENS that Bergoglio does.  Recall also that not every error = "heresy" in the strict sense, in the sense that would remove from the Church.

Secondly, when does heresy become manifest to an individual's conscience?  Only by the intervention of Church authority.  I've gone through the whole thinking on this subject only to have it ignored.  Perhaps I can try again here.

Thirdly, there's the inconvenient matter of there being an entire school of thought contrary to the Bellarmine opinion which believe that papa haereticus deponendus.  You bloat the Bellarmine position to the level of being practically de fide truth when it's just one opinion among many on a very thorny issue (as evidenced even prima facie by the range of opinions on the subject).

If it was THAT slam-dunk and straightforward, then why should there by five or six opinions on the matter by reputable theologians?

The fact that a public heretic cannot be a Pope is a slam dunk and is that simple.

But those whose truly believe that he is not a public heretic or are invincibly ignorant of the above fact cannot be considered non-Catholics.  

No, it is not.  This shows bad will on your part, and stuff like this is what leads to many of the bad fruits evidenced by sedevacantism.  Was Cardinal Cajetan invincibly ignorant of the matter?  No Traditional Catholic, however, can be said "invincibly" ignorant of the opinion you hold, since it's an ignorance that CAN be overcome.