As someone who was a casual Metallica fan then, I saw the hate, but it always seemed to me to be something similar to what happened with REM and The Police. They were a niche band with a devoted following who got a little bigger, and most fans went along with that, albeit grudgingly, but then they hit a whole new plateau and the hard-core fans got resentful. That was compounded by the change in image - look, let's not beat around the bush, sexuality was still a little dicey in '95, '96. Halford had not come out yet, for example - and people were confused, and angry. I think the music was made to suffer for other things, but the backlash WAS real.
Add to that the Napster thing, since I don't think today we appreciate how much of a pariah the band - and Lars especially - became after that. It was hard to look at that as anything other than a money grab, even if he was right, and even if he did see the future accurately. I know I was so thrilled with Napster, and once I got broad band it was "kid, welcome to candy store". I had fake rules for myself - I didn't download anything I either didn't already have in some format (vinyl/cassette) or that was unavailable otherwise (I think I have about 25 versions of Raving And Drooling ("Sheep"), You Gotta Be Crazy ("Dogs") and Shine On You Crazy Diamond from their '74 tour floating around somewhere) - but it still smacked of running afoul of the ethos that Metallica stood for. I remember reading articles about Lars making cassettes of songs from Diamond Head and others early on, and I didn't see the difference, then.