No one said it makes game 'easy' it just is that some people would rather not have it.
Actually in this current state, you do not need an icon, it is SUPER obvious what mobs attack you.
if you see a giant scorpion... you can assume its aggro.
Some mobs that attack you don't have the icon for some reason...
Everyone knows that mobs have a aggro radius, that is a simple logical conclusion, without a restricted radius they would attack you from miles away. Also the range may get smaller if the level difference gets greater.
You are the close minded one, you go against ideas and wishes of others without even having played the game.