I think the ones who say it shouldn't be nerfed are the ones who barely go up against AD Dark Harvest and/or never play ARAM.
Since every harvest is separate for each player, anyone can use it and since just farming minions on Normal or just playing ARAM (since minions on both side are on 1 lane), getting high stacks fast is easier than actually farming. And if you wanna justify it, then try justifying this:
How is it fair that a full armored tank takes 800 damage from a single AD attack?
There seems to be no reason to build armor against DH champs because not only does their damage stack far quicker than you can build armor, they can keep stacking it. This makes snowballing champs even worse to play against, especially with Kha'zix, Rengar, Shaco or Ezrael, the damage they do with a single skill is quite frankly, not fair. There is literally nothing you can do against that other than dive in with your team on the AD and pray to God you have some health left for the rest.
I think on Normal it is quite bad already but on ARAM, it's just impossible at this point. Why not put a max stack on it? Why not a max extra AD? Or why even stack both AD and AP and at 25 and 20% each plus your stacks? Again, this just makes snowballing champs harder and harder to stop and makes the game so unbalanced.