I have used pleasant in a wrong sense, and you are right, sometimes art is unpleasant to look at. But here's the thing. The art being shown is meant to look unpleasant, and people have to feel uneasy and somewhat mortified, and the artist has succeeded in conveying that pleasantness. Bad art will try to convey the same thing, but come off as "hilariously bad", which is not what the original artist would have in mind. Do you get what I am saying?
personally i don't think i know enough about that piece or Francis Bacon to say if he meant it to look unpleasant.
let me just focus in on what i take issue of so my points don't go too off track, this thesis you've said:
That's how a drawing should be. If a normal person cannot comprehend or understand what he or she is looking at, or is being given the wrong message that the character is trying to convey with their audience, then that drawing is a failure.
this set of rules applies only to a specific medium. I'll give a couple layers of abstraction - it applies to Bambi, thus it applies to Disney animation, thus is applies to mass-appeal, popular animation.
But these rules you've said to not apply to all art. If someone can't tell where the thumb is on a drawing, the drawing is not a failure, and especially, if someone's art does not follow these rules you've laid out, that doesn't mean it's invalid, IE "that's how a drawing should be".
This ties back to what i was saying earlier - if someone's picture is not anatomically correct and they say "it's just my style", being so invested in that statement is pointless. Give criticism to those who warrant it. If they're not receptive, don't pay attention, instead, find the art you enjoy and share it to the world. From what you've laid out, your idea of good art - there's tons of it out there, and there's no need to be so concerned with what you don't think is good.