Tangent to this: I think it's often useful to allow suggesting "bad" solutions to vague problems because good solutions often hang out close to the bad one's and shines interesting light on the problem. Or bad solutions often immediately provokes better ideas. If you immediately see that a proposed solution is bad there's a good chance you know what specifically is bad about it and can propose an amendment.

Suggesting a bad solution is sometimes half the way to a good one.