And of course just saying anything negative got the 4E fans enraged and vice versa. That is the root of all edition wars. That fans get over protective and take other people not linking their edition personally. It is like they take it as they play the game wrong.
That is definitely part of the problem, but I'd say the root of edition warring is, in fact, the common belief that one's own opinion is the only correct opinion. Anybody disagrees, well, they must be stupid or shills.
This also leads to the worst part of edition warring, when people actually insult each other for liking the edition they don't. I've seen new players driven away from gaming altogether by the sheer hostility of other gamers for daring to pick the wrong edition as their starting point, even if the old edition isn't for sale anywhere.
This isn't limited to RPG editions. It's the source of just about every type of fan war. Xbox versus PlayStation, Marvel versus DC, PC versus console. Heck, sometimes there's even no versus. I have been repeatedly and viciously insulted for liking the Star Wars prequels, even when I agree the original trilogy is better.
Then there's the other half of the equation, those of us who don't think this way, but have been insulted for our opinions so many times that it becomes instinct to think someone that disagrees with us is insulting us. That's where the protectiveness you mention comes in, I believe.
Edition wars, and fan wars in general, would be a lot less serious if people on both sides of this equation would recognize this in themselves and tried to empathize more with others. I know I try. Sometimes I fail, and get drawn into the arguments, but a lot less often now than I used to.