Well, I agree that Simon is sometimes too nervy especially with negative critiques. However, the contestants' appearance is very important and Simon's advice usually helps. For instance, look at Lakisha! She took Simon seriously instead of being offended and has greatly improved her appearance! She looked stunning in the flowing white, floor length dress last week. When one knows they're wearing clothes that compliment them, it helps their self-esteem, thus their performance. (in most cases)
But, the outfit also must be comfortable!