I don't think down arrows would be enough. Unfortunately a lot of new Ask YC posts are opinionated and people vote as means of identifying with the post rather than as a measure of interest or quality. Its interesting how well the poll system reverted the up arrow to a quality measure rather than an agreement measure in polls.

Most of the objectionable AskYC posts could probably be shoe-horned into polls by editors - just with 'agree' or 'disagree' options.

Maybe every post could have additional [agree] [disagree] buttons, because a lot of poor quality submissions are equally opinionated.

The missing thread-level down arrow does prevent reddit-style polling. Pg might not like this suggestion because a worse nightmare might be "vote up if you like candy" threads.

If the down-arrows were karma-restricted to ensure adequate assimilation, though...