There appears to be two very distinct groups of players- people that have solely/mostly only played FFXI and people that have played other MMORPGs either as well as or exclusive of FFXI.
As a FFXI player myself (and having personally not played any other MMORPG), who was used to the "way things worked" for the 5 years I played, it is sometimes difficult to distance my gaming experience of FFXIV from that of FFXI. The temptation (and probably human nature) is to compare it too much... I still do it now, and sometimes I have to force myself to take a step backwards.
My rambling point?
I think this is why those that have come only (or mainly) from FFXI are quite against having the aggro icon at all as they feel it makes the game too easy. I will admit, after not having this aggro icon feature in FFXI and having to get used to which mobs of which family aggro by what means, my first initial knee jerk reaction was that I didn't like it. Obviously people coming from other MMORPGs where there is a system like this in place will have the exact opposite reaction.

I can understand why they have put the feature in; do I like it? Not really. Would I ask them to remove it so that players "have to learn" about which mobs aggro? No, this is not FFXI. But, as with everyone else I hope that they either redesign and make the icon easier on the eye and smaller and/or allow the icon to be toggled on and off.

Last FFXI and FFXIV mob aggro comparison..... I personally would prefer to have a "Check" mob selection to see whether they are passive or aggressive, which would be less intrusive. I know it is not an instant visual feature, but if you are unsure of a mobs aggro range and behaviour are you really going to run straight up to it anyway?