I think we have all been, many a times, defensive about our designs.A design is like a baby, something we visualised and throughout the design process,kept adding features to it. After much time and effort, the design is born.
When someone criticizes a mother's child, she feels sad, hurt.Similarly, when someone points flaws in our designs, it feels awful.So much care and attention was put in formulating the design, that at the end, we cant bear to have someone criticising it.