Hmm.
Personally, Harley terrifies me. She's everything I hate about the expectations that go with being female - that "stand by your man and be cute and perky" riff never did sit well with me. Yes, I'm aware that I just described much of her appeal to some guys. I'm not interested in appealing to those guys. I don't assume that Harley cosplayers are solely motivated by appealing to those guys either.
I kind of think that this is a shallow interpretation of her character. Now, I'm no expert on these matters, but I've always thought that she was simply a tragic figure and that her entire motif with the painted on clown smile and chirpy insanity was sort of riffing on that - you know, putting on a happy face to mask what is essentially severe emotional trauma.
This is actually a bit of a reoccurring theme in Bat-Man comics in general and not just with Harley. I mean, the Bat himself actually does the same thing for almost exactly the same reason. He puts on the cowl in order to escape the feelings of helplessness and rage that he had as a child.
In this light, I think it's worth reminding people that co-dependant relationships aren't actually just one way. The person who is in the position of someone like Harley Quinn is getting an emotional need met by acting out this way. Now, it's not a healthy way to go about doing this, but this is in it's essence
why the character does this stuff. Instead of thinking of her as a brainless bimbo and slave to the Joker, it's actually more appropriate to imagine her more like someone who would be a heroin addict and unable to break their addiction regardless of how low it brings them.
Honestly, I think this one panel from
Injustice, as short as it is, really drives this point home about the character.
Obviously people are going to always have their own interpretations of characters, but I think when people merely dismiss her as a chirpy bimbo, they're kind of not getting the point.
Anyway, as far as Cosplay goes, I think the vast majority of people are merely interested in the aesthetics of whatever cosplay they choose to do (and the craft as well that goes into the costuming). I think Harley is probably very popular because she's quite fluid in how she can be portrayed - from "cute" to down right "sexy" depending on how comfortable you feel about it, and of course, she's "wacky" a lot of the time, so that's probably appealing to people as well (Who doesn't like to cut loose?)
I guess my feelings are two fold: I think the critics are probably getting her character wrong on a lot of levels and I think their criticism is a bit misplaced since I doubt that the "messaging" they think is implicit with the character is even being "received" by people. Most people probably don't even have the personal context to even understand it, let alone absorb it.