After that we have established that the homework is okay and fine, comes the question should be allow it to be "standalone"?
I think not, I think that we cannot allow questions to be labeled just as homework without at least some other indication about the topic of the question.
I agree that sometimes users don't know exactly which tags fit their questions, (e.g. using logic when just wanting some help about a number-theoretic puzzle or so). In the case of homework it is virtually impossible not to know how to tag your question: start by the course's topic, it's usually straight forward and gives some information.
Is it even possible to have that? (somewhat like the meta doesn't allow posting without one of the mandatory tags, only backwards)
Addendum:
Going through the last month's question under homework I found ten questions whose only tag is the aforementioned tag: one was migrated and then deleted; one was closed as a duplicated; The rest fit into different possibly tags:
- solving quadratic equations by completing the square
- How do I show that there exists a real number that equals its cube plus its square plus 1?
- Torsion or Non-Torsion subgroup of $H_i$ do not define a homology theory.
- Order of precedence: in $ab^{c}$, which operation goes first?
- recurrence relation on bank interest
- Finitely generated field extensions
- Problems with euclidean GCD
- Understanding difference equation