I think the series would suffer the Need For Speed effect: people would be confused about the series' many changes in a short time: From the insanely arcade physics of Vice City to the 'Realism' of V (Not actual realism, just compared to Vice it is), then there are the arcade Stories, and then the Realism of IV/EFLC, and finally the Arcade of San Andreas. This could make fans very confused.
Also, this would mean GTA:Online in 2004. Sure, there were Multiplayer titles in 2004, but GTA:O would be too ambitious for the time, specially for consoles like the PS2 that didn't need to be plugged to Internet, it would make it very hard to download updates. Also, this would mean 'Shark Cards yo!' in 2004, which, if it was at least slightly successful, could change the way the series is. Maybe GTA IV's multiplayer would also be made around Shark Cards, and maybe even San Andreas would get the same threatment.
As for the people who disrespect a game or another without actually playing it, they are afraid. They are afraid of new experiences. "What if that new experience is better than the thing I've been cheering and fighting for my entire life? What if my enemy is correct, and I'm not? I don't want to be incorrect. I'm a human, I want to win." This causes biases and people fighting eachother without actually understanding the other's point of view, in a way RCR can explain better than me.