Consider a question of the following form.
I have an idea about XXX...
---Description of Idea---
Can you spot anything incoherent, illogical, or especially problematic about this idea?
Do questions such as this belong here?
I don't think we've ever made an official policy on those kinds of questions; we have allowed them, historically, although typically only those with short, concise problems. If one was to ask us to spot a flaw in an entire research paper or something, that would be a different story. The key is keeping it to a reasonably scoped question where you are focusing on the logical form of a single argument.