Why is Kant's practical reason for God wrong?

[Faith No More]

From the little I know of Kant (and someone correct me if I'm wrong) but a major compenent to his critique of metaphysics is that what we experience as reality is but mental recreations, our perceptions. Since we only ever, and could only ever, know the perceptions and not reality, we can't say anything about what (if anything) is behind those perceptions and the reality therein.

Would that be an accurate assessment philosophy people?

That seems to be fairly accurate of what I have read. The way it was posed in what I was reading was that Kant believed our perceptions are like eyeglasses, in the sense that all of reality is filtered through them, and it is impossible for us to understand reality unfiltered.

But given that, I'm wondering how he justifies his moral and theological stance.