What does keeping track of mileage in your head have to do with recalling which mobs aggro and which don't?

The aggro icon itself isn't the issue, it is the mentality people have about it. What is so wrong about it? Is it because it is ugly, or because it is too helpful? Any feature that makes the game easier to play gets large amounts of hate from the Hardcore players. This is true of all games. The reason people hate the Aggro icon (Other than it being ugly as Gary Busey) is the simple fact that Hardcore players don't want the new players to have a luxury they didn't have.

Before they changed the SP system, I was a R20 GLA and R8 Sentinel. After the change, there were people who just started ranking their GLA that had already surpassed my SNT Rank simply because they were leveling with the new system. This pissed me off. Why? Because they had it easier than I did.

Same case here. Anyone who has spent time with the game knows what to watch out for, and the fact that it is now obvious as to what aggros and what doesn't makes it easier for newcomers, but was a luxury that we didn't have previous to this patch.

So really...it call comes down to two reasons: The icon is ugly, and it is N00b Friendly.