Dalamar said:
Crap has always gotten approved, and good things have always been deleted.
Crap getting approved is why we have flags. Good things getting deleted is why we have appeals. You're welcome to do both.
Making bad_quality act as a "deleted" post that can be manually searched is just fine. It's not like it would consume more space since nothing is deleted anyways as it is.
We don't have a "bad_quality" tag. There was a fairly subjective poorly_drawn tag once, but it was removed once it was decided that badly drawn art should just get flagged instead. Questions of quality are better left to trusted approvers than put in the hands of any user who can add or remove tags on a whim.
Also, I don't think tags work the way you think they do, i.e "won't show unless actually searched for". We don't have any tags that are hidden from everyone by default. It probably wouldn't take too much effort to code a special type of tag that does this, but I don't see a reason for this when we already have status:deleted.