The obvious thing to do would be to downvote answers at sight, without a comment. If done often enough, this is already a deterrent to answering.
Then there are a few options:
- 20K rep users can vote to delete negatively scored answers. (Which is another reason why downvotes are helpful). However, the number of 20K+ users is not huge, and not many of them will want to do this.
- 10K+ rep users can vote to delete the question (which of course deletes any answers to it).
125+ rep users can downvote both question and answer enough for automatic deletion to happen. Since the question has at least one answer, auto-deletion requires several things, in addition to question being closed (full details here):
- Question score $\le 0$
- No answers with a score $> 0$
- No accepted answer
This not going to work every time, but can be sufficiently discouraging if applied consistently.