One possibility that comes to mind: you can spend 1 (maybe this number can be increased in high-traffic contexts) karma and forfeit your ability to gain net kar

One possibility that comes to mind: you can spend 1 (maybe this number can be increased in high-traffic contexts) karma and forfeit your ability to gain net karma on a specific comment, to force people to reply to it in order to downvote it. Something like this is pretty obviously necessary at this point; it is trivial for me to find examples of bad-faith downvotes that cannot be backed up with argument, and it shouldn’t be.