This norm serves a great purpose in that bad ideas can be debated and debunked. However, it also kills a lot of good ideas as well.
FIX: Stop yourself from first pointing out what's wrong in a situation, and make it a habit to jump to what's right instead.
If an idea is simply rotten, say how much you appreciate the thought or effort, and explain why you feel it falls short and how it can be improved. If you kill it, provide an alternative.