ASK PG: Why can't you bury or downvote submissions?

If a submission is offtopic it should be killed. Hence flag. If a submission is on-topic, you have to depend on votes to rank it. It seemed from watching Reddit fairly closely that downvotes were, on average, made more reflexively than upvotes. So we just use upvotes.

If it aint broke...

Honestly I think that's something to consider in the event of a decrease in quality. The current system is working fine at the moment.

The flag option suffices. The curators here do a good job of looking at all flagged submissions for whatever problem they present. You may not have heard that a submission that is flagged a defined number of times by users with power to flag will be autokilled, removing it from view of users who don't have "showdead" turned on.

'you' can downvote submissions, but You (&I) cannot.

If I recall, there is a certain user point threshold over which downvoting is enabled.