The backlash against booth babes is the result of a perfect storm of jackasses trying to push their views on the industry. Long read ahead of what I understood the motives behind that backlash.
On one side you have the classic gaming nerd sort. These people have watched their hobby and fandom be pulled into the mainstream and then slowly changed and pandered to the wider audience. What often made their hobby enjoyable has been steadily removed in the name of industry claims of "wider appeal" and the like. This says nothing of gaming's previous scorned status, the usual magnetism outsiders have towards games as a way to feel a sense of culture and community and a means to take pride in outsider status, as well as the constant attack the hobby has endured by political demagogues and religious asshats. Seeing the newcoming, more casual and accepted group of gamers, they put two and two together and blame this rise of gaming into mainstream culture and all subsequent pandering on the newcomers. A segment that has not had to put up with the crap they had, who do not share the same degree of passion and who outside of their enjoyment of games are otherwise the same sort who ignored if not outright mocked and attacked the hobby not long ago. The usually isolated group of gamers often then closes ranks even more and starts viewing people as invaders and cultural appropriation, with the most easily visible ones all the more quickly disowned, if not attacked. This started the whole "fake geek girl" mentality I imagine.
On the other you have a growing segment of gamers wanting the medium to grow and develop, to push out of the isolated mindset, be more accepted and be take seriously as a mature art form and entertainment. They see much of the industry's attitude towards customers as revealing how little they think of their customers, and quickly point out such behavior as bad for gaming as a whole. A cancer to be marked and removed. A large one often attacked is business practices that try to milk customers of money rather then treat games as a form of viable entertainment if not art. As such advertisement that reduces a game, even a good one, to cheap pandering is looked down on when not outright attacked as merely being a way the company is trying to borderline scam people out of money, especially true with products that are otherwise complete crap.
Add both of these mindsets, and one of the few things they agree on is that the booth babe doesn't fit. The first see them as a representation of the very sort of person who is changing their hobby. They know little to nothing of the hobby, are paid to be there and are surrogate for the countless "fake" gamers out there who have contaminated something they love and are slowly destroying things they care about strongly. The booth babes represent someone who should not be around their hobby. This is often not even because they are attractive but rather because they lack the same passion and dedication yet are trying to still sell you a product. The events are no longer geeks and nerds trying to share a passion and sell you on something they love (even if the passion is fake), but a full blown "shut up and listen to the sexy model" bit of advertising that has been done to death in every other form of media. Games are treated as nothing special, just one of another sort of money making. And while they may always have been so, the booth babes represent the epitome of industry no longer even caring enough to put on the illusion, no longer seeming like the same sort of geeks that the core gamer thinks they are.
The second see the booth babes as the height of industry scorn and pandering. The industry only sees gamers as horny stupid easily distracted teenage males, thus displays of skin by models catering to exactly that idea are harmful towards making games as a whole better. They represent an older time in gaming history and beg the question of how games can be taken seriously as an art and entertainment if all anyone ever sees is industry pandering and sexy models. Thus something should be done to force the industry to not resort to the lowest common denominator in advertisement and instead stand more on their own merit, rather then who they can fit in what skimpy outfit.
While there is obvious flaws with the mindsets above, that mix does seem what fueled most of the resentment and derision towards the booth babe phenomenon. Not sexist (for most gamers), not resentful towards the models themselves even, but what they represent, be it the ever growing pandering to a casual gaming audience because games are the latest in a long line of subcultures that have been pulled into the mainstream and bastardized or because they represent the pinnacle of industry resentment and dismissal of both the audience and games as an art or entertainment form beyond just making as much money as they can out of every property or game.
There is a correlation between the industry's steady alienation of their own core players through bad practices such as more and more visible greed and trying to make all major releases so same; and the rise of the disgruntled and assholy gamer retort towards perceived "outsiders".
TL
R
the isolationist outsider gaming subset and the optimistic, wants-games-treated-like-mature-art gaming subset both agreed with each other that it was bad for paid female models to be used for the purpose of pandering just for cheap attention and easy advertising, albeit for different reasons.
