Now that question downvotes are free, why do we need a flag? Should 'low quality' processing be simply triggered by a sufficiency of negativity? If you think a question is low quality, downvote it. If the score reaches, oh, -2 or -3, set loose the dogs of raw.
I see a fairly large number of low quality questions that I flag and which are closed by a moderator, that never receive more than one downvote -- mine, right before I flag.
It's not a bad thought to have a flag automatically raised when a question goes sufficiently negative, and I agree that more downvoting and maybe a pamphleting campaign about same would be good for the site. I just don't think that the flag should be removed. Supplemented, maybe; eliminated, absolutely not.
Also, the value of "sufficiently" would have to be pretty negative -- I'd say -6 at the absolute maximum, probably more like -8. Voting is supposed to reflect the quality of the post, of course, but people vote for all kinds of reasons, and lots of unwarranted automatic flags sounds like a great way to frustrate the moderators.
While generally low quality questions should be edited, some of them are too unclear for anyone to edit. Those who don't have the ability to close, need to have a way of flagging them for attention. The text at the end of the explanatory sentence for low quality is
Of course only a moderator could do that.
While I haven't used the reason a lot, since I usually edit those questions, I have had to use it a few times. For answers you have the 'Not An Answer' flag reason, but we don't have a 'Not a Real Question' flag reason, it's only a close reason.