If they do decide to keep it I would approve of making it both toggle-able and not start with knowing all the info.

I would suggest making it so when you start the game no mob is known as being aggressive or not however after it aggros you once it will be added to your aggro list at which point you will be able to tell whether it aggros or not through this system.

This way the people who need/use the system won't be killed over&over by the same mob even if they haven't been to a zone many times or in awhile however at the same time they will have that experience of learning for the first time and veterans/hardcores won't think less of those people as much.