So, lemme get this straight..
You don't want to see the icon, but you don't want an option to turn it off, because others will see it and it will ruin your sense of adventure? Really?
There are lots of people who actually like this feature. A toggle is the way to please both.
Why should they remove the feature just because you don't want to use it and you don't want anyone else to use it too?
I miss the FFXI adventuring feeling - yes. But a toggle should do the trick. I actually walked to Mor Dhona yesterday and I laughed at myself because a lot of the mobs I thought aggroed (before the icon was implemented) didn't XD