If everyone uses all the DV mana they have, the blockchain is still functional (even more than today because user preferemces are shaped better).
I agree (sort of). If downvotes become universally utilized to their maximum potential by everyone, then it simply becomes an inverse vote. However, the challenge then becomes how to maintain curation rewards. Because the DV can be sniped against a nemesis just before payout (to maximize the effective penalty), but the upvote cannot (well, it can, but at a greatly reduced curation percentage).
So, it ultimately becomes a battle of DV bots, and incentivizes the average user (author and curator) to figure out how to avoid the DVs (by not making anyone angry, and by not getting 'upvotes' from accounts with a hefty DV following them).
Hive becomes a Mad Max style lawlessness, where warlords fight each other and average folks just try to keep their heads down and stay out of the line of fire.
I fail to see how that ends up being positive or beneficial.