I think that the icon is a great idea, am all for exploration and all that and the icon helps to know what mobs to avoid and which are safe. Some people's "learn it your self" ideology, is others frustration. Best example, even at 50, there are thing that can easy kill you, so imagine you spent the last hour ruining from camp A to get to camp B and 3min before you hit camp a you come across a mob. With this icon you can know if you can pet the mob and move on, or take 3min extra to go around it, instead of having to rerun from the start.
I do agree that we need a toggle on/off for the icons, not only for mobs but for quest npc. That way some can learn the hard way, some can cut out frustration.