The icon is very practical for me, because I don't usually play in parties, so if I go near to an enemy and turns out that it's aggressive, it often kills me with one hit. I like the warning, because I don't have much time to play and I don't want to wait 2 mins to reagain my HP after a death.
Sounds like a good solution to add an option in the configuration menu to turn it on/off, if there are players who really don't like it.