They're talking about things of which they don't have the slightest understanding, anyway. It's only because of their stupidity that they're able to be so sure of themselves.
In Paradise, as always: that which causes the sin and that which recognizes it for what it is are one. The clear conscience is Evil, which is so entirely victorious that it does not any longer consider the leap from left to right necessary.
The crows maintain that a single crow could destroy the heavens. There is no doubt of that, but it proves nothing against the heavens, for heaven simply means: the impossibility of crows.