Actually Jim it would have been nice if you addressed the actual issue. Interestingly you don't touch the issue of the reception less attractive, or those of average apperance, receive in comparison.
You also seem to miss the point that the arguement "they aren't hurting anyone" doesn't apply here, you say you can't understand how this hurts anyone, but if that's the case I can't help but wonder how closely you've listened to the actual complaints.
The rage over the "fake nerd girls" is pretty much about exploitation. The basic idea being that if you have a hot girl promote something, it's going to manipulate men into spending money on that product or service. If you put a hot girl into the equasion on a product aimed at a male demographic famous for not having any luck with girls at all, it's even more effective. That's advertising in a nutshell, and in of itself wouldn't be that big a deal, IF it wasn't being directly tied to the whole "Camwhore" phenomena and other internet honey traps. The idea being that a fairly attractive girl, seperated by the barrier of The Internet, but able to promote herself, can insinuate herself into communities of people starving for female attention, and then parley her attention into gifts and benefits, through generating "hits" for a channel if nothing else. Some of the contreversies over online gift or "wish lists" have also circulated around girls doing this kind of thing using such services to receive their payment.
The anger in this case isn't so much about wanting to keep "fandom" male only, so much as it is that most of the guys getting upset wish that there were attractive women into this stuff, but there are so many fakes that it has become expected.
There is also a little more to the "cred" involved than you, or other critics speaking against this, want to give credit to. A nerd is by definition a social outcast, a pariah, a hermit, who is scorned by society. Someone who by nessecity takes escapism to extremes, and winds up becoming an expert on a lot of this kind of media. A greater-than normal interest in comics, video games, or whatever does NOT make you a nerd or "hardcore" in this context. Your attractive girl by definition can and does fit into society, and that creates a barrier that is hard to overcome, not to mention means that the person is going to lack the focus to become the "real deal" in regards to the media itself. To put things into perspective here if you look at a lot of these "Nerd Girl Responses" people have been trying to get to catch on, like oh "I haven't read every issue of Batman, and neither have you", kind of miss the point that a real nerd who is fiaxated on Batman probably HAS read every issue of Batman, going to extreme lengths to obtain scans if nothing else. What's more it goes further than that, let's say "hot nerd girl" is an expert on Batman and has more than a passing of interest, understand that the REAL nerd is probably also an expert on half a dozen other things to the same degree. This occurs because the Nerd literally has no life in a traditional sense due to beign a Nerd, a pariah, an outcast.
Also I'll point out that men DO get the same kind of responses, with gaming and "geek culture" becoming a bit more popular, there has also been a backlash against "casuals" in general and in paticular against the "Bro" or "Fratboy" involvement in gaming, to the point of that group being mocked even more than the false nerd girls. It's just that you see less desperate nerd boys wanting to white knight some jock.
Basically, if your one of those who can claim to have a life other than gaming or "nerd media", a solid circle of friends you deal with in person (as opposed to other nerds you deal with at a safe distance), and similar things, then your really not a "nerd" in this context. That might not bother the nerds if it wasn't being used for purposes of manipulation, or if you didn't have people demanding and receiving "cred" as nerd-culture experts when they hardly fit the bill.
I guess what I'm saying is that the nerd-cosm is a refuge for the pathetic, now that it's producing something that society is beginning to value, there are attempts to take that without the rest of it. Not to mention is that your typical outcast longs for acceptance on their own terms, when you get some attractive girl or "Bro" doing research on a subject over Wikipedia (the obsession of Nerds in catalogging their favorite forms of escapism has contributed to the problems) and then acting as a spokesman for "Geek culture" as opposed to a REAL, pasty, obese, acne-covered, behemoth of a geek, it breeds resentment. Being a big, fat dude Jim you have the advantage of being someone who fits the stereotype, by your own admission, you are a member of the club, or at least can pass.
Yes, this is pretty damning towards nerds (arguably my own people, especially now) even as I say it, but it's the truth.
The question of whether an attractive girl could ever truely be a nerd IRL is a subject of debate in of itself. It can be argued that a girl who is conventionally attractive always has the option to be accepted by society as long as she remains attractive, which prevents her from ever truely joining the "nerd herd".
Also don't misunderstand, nerds love their eye candy, booth babes are something a lot of nerds have defended. Just don't try and present the models as being nerd girls. Nerds can accept and appreciate the advertising (even if more aware of it than I think those presenting it would like, which is half the problem, nerds are a paranoid and hyper-aware bunch).
Oh yes, and also Jim, you might not be aware of this, but among Nerd culture when it comes to "Nerd Girls" on the internet who are not tied to a product, there is a sort of game going. When one of these shows up you have the nerds talking to her sort of side-betting privatly on how long it takes for her to try and get something out of them. This is actually sort of what spawned the entire "Tits Or GTFO" meme, since flashing their boobs is one of the things these girls eventually work into their routine in their effort to exploit you. The girl shows her boobs, and she expects something from you even if she's subtle about it, with the implication that you need to make her happy to see them again (or perhaps hints of more), it can be done in differant ways. The meme is kind of a "let's cut through the chase, we know why your here".