While you are correct to point out that quantitative changes can concatenate to create qualitative changes, free is simply less expensive. TBQH the downvote pool isn't free at all, since it comes at the expense of other benefits that would otherwise be paid from the pool, in exactly the same way that free healthcare, college, or any other welfare proposal isn't free.

However, I do believe it will result in qualitative changes. I foresee the development of a market for downvotes, and this will have an extremely negative impact on Steem society, as have all other automated voting mechanisms.

We will indeed see what comes of it.