People who want mob density to be higher are the ones capable of doing mp 10 with their eyes closed.
These people want to earn good cash, because frankly, more mobs = more chance of loot dropping, these people also don't want a hassle to run around for 10mins and only killing 10 packs of mobs....
What they want is an army of demons continuously rushing towards them while they use their infinite resource skills to slaughter them, without even moving.
This mob density option, if there's no limit, it will create a damaging gap for people who don't currently have the gear. People who don't have the gear will never have enough $/gold to buy the best in slot gears with highest roll, because those items will be forever at the highest possible B/O price, while whatever they farm(with low mob density) will never sell in the AH.
In short, implementing this 'mob density' option will end up in a familiar scenario in the real world: The rich gets richer; the poor gets poorer.
Even if that is fine in Blizzard's eyes, the gameplay will get boring, and people will start quitting after they are sick of spamming the same spells non-stop for 15mins.
I mean, how lazy can people get? I know it sucks to run around in a maze trying to find mobs, but i think it is fine, it's like a tiny balance. You have infinite resources, but not everyone, that 5seconds of running around without any mob is actually a good space of time for people with less gears to regain some of their depleted resource.
Edited by Marc#1660 on 1/24/2013 4:34 AM PST