Yeah, it's a really tough question. I guess in each case we need to audit why people are missing the point. I wrote something a little about this in an essay about
Starship Troopers, of all things:
And that, I think, is where the defense of the film breaks down: it mostly consists of simply pointing out that it has satirical ambitions, and then assumes that the number of people who don't realize this must be evidence of its brilliance. But the quality of satire is not measured by the number of people who don't get it. There are two reasons satire can fail to land: because it's way too smart, or because it's too simplistic. It can go under people's heads.
I think
Full Metal Jacket can be fully (heh) absolved, because it's not really ever "fun" to my mind. I think someone misinterpreting that film is
really misinterpreting it.
For
Harold and Maude I'm more inclined to place the blame on viewers if I'm forced to pick just one or the other, but I think it's a bit of both. I think maybe the strength of Ruth Gordon's performance is a confounding factor in that it maybe makes the character more sympathetic than she should be, in total. That actually might be a part of all the examples you listed (both in text and with the image): if the actor is effective and charismatic enough, the line between admiring the performance and admiring the character maybe gets blurry.
Just for the record, I haven't been able to find a definitive answer to this question I'm fully comfortable with. It's an interesting discussion which I've thought a lot about, but haven't had enough time to think over fully.
With
Full Metal Jacket, some things I think could blur the line are that R. Lee Ermey's performance feels more charismatic than hateful towards the men in the boot camp or that some of the insults he uses are, admittedly, pretty clever and (in a vacuum, to be perfectly clear) funny. I think this is why many people find that segment funny. I suppose, if Ermey showed more anger towards the men and if Kubrick wrote far less one-liners into the script, the rate of people misreading the film might have dropped.
I agree that acting could be a reason why this is the case for
Harold and Maude. Gordon does have a sympathetic performance (although, I think this is fitting considering that she embraces life) and somebody could definitely get hung up on that and not consider how her behavior is negatively impacting other people around her.
For me, I'd actually say it's easier to absolve
Harold and Maude than
Full Metal Jacket for people misinterpreting it. Even if there's concrete evidence that a film isn't idolizing a character, it is possible for a movie to influence this backlash depending on the presentation of those characters.
Harold and Maude has some of this with a rather quiet, sympathetic performance from Ruth Gordon.
Full Metal Jacket has quite a lot of factors which blur the line with a thoroughly charismatic performance and some frequent clever insults.
One final thing I'll address is I think most of the films and shows in the pic I posted upthread (I haven't seen
Rick and Morty, btw, so I can't speak to that show) will have at least a couple factors which blur the line. With
Scarface, Tony Montana is portrayed as a wealthy, cocaine-snorting badass who can survive multiple bullet wounds while everyone around him gets either killed or is rendered incompetent in a few seconds of being injured in firefights. Or with Walter White, he's portrayed as a rich genius who knows more about cooking meth than pretty much everyone else he meets on the show in spite of them being in the drug business far longer than him. Really, I think most films which have a reputation of fans falsely idolizing characters they aren't meant to idolize will blur the line a bit, even with concrete evidence that the character isn't a good person. Whether it's a case of acting, portraying them as smart, or having them do something cool or badass, I think this will always be present. Is there a line when this goes too far? Perhaps. Do I know what the line is yet? I'm not sure, to be honest. It's a tough question and I'm not sure I'm read to criticize any of the films or shows I brought up so far. I'd need more time to think that over.
For what it's worth though, I think
Harold and Maude is less guilty of this than
Full Metal Jacket is