In my opinion it is not only OK, but desirable. I will not reiterate the things I already said in the linked question. But I will comment on the main argument towards keeping this tag alive: its usefulness.
While I agree what the tag is useful (every time the tag is used, it's something that belongs to a discrete mathematics course), it's usefulness derives from its meta-tag properties.
Tags are supposed to be mathematical in nature. Meta-tags such as (faq) and (homework) are undesirable. The tag (discrete-mathematics) is pretty much useless when it comes to its mathematical description. It's only useful because it's named after some courses. This is social, not mathematical. As a course's name it might even be OK, but we have much more expressive power here on MSE as we can have several names (tags).
What I suggest in this paragraph doesn't fix the problem, but at least it makes for better tagging. I think it shouldn't be allowed to tag questions with (discrete-mathematics) alone, the same way one can't post questions here on Meta MSE without the appropriate tags, the software won't let you. A user trying to post a question with this tag alone should be prompted to pick at least one of this tags: (divisibility), (modular-arithmetic), (elementary-number-theory), (combinatorics), (logic), (predicate-logic), (propositional-calculus), (graph-theory), (recurrence-relations) and I'm sure there are others that could be added to the list.