I don't like change. But I guess it has merit. (An answer downvotes graph would help to judge it better..)
Usually I avoid downvoting newcomer questions. It's pointless to downvote a rep 1 user. And if it costs me -1 without affecting that account, I do in fact opt out. (But most people use closevotes in lieu of downvotes in these cases anyway.)
So making that free would indeed incentivize me to downvote more questions. But I believe I'm already downvoting too few answers. And if this idea is given a roll, I would request that this is used to at least even out the discrepancy between question and answer votes:
cost upvote cost downvote
question 0 +5 0 -1
answer 0 +10 -1 -2
If upvotes only bring half as much reputation win, then downvotes should subtract only half of what answer downvotes do. And I assume it would cause less hurt feelings if the free downvotes cause less loss there.
Regarding the pity upvotes that's maybe not such a glamorous idea. Albeit there is the same discrepancy of worthless internet moneyrequiring 5 downvotes to cancel out a pity answer upvote. (And dangerous answers IMHO require fiercer eradiction than unreadable questions.)
(The banning metrics would be unaffected by the reputation charges. It's the downvotes alone that count.)