Why do Americans only tolerate positive criticism, thoughts

[Mr.Darcy]

I find myself that I have to bite my tongue a lot with most Americans. Some Americans will turn hostile if you give them negative criticism or tell them that this is a bad idea. According to them, having a good attitude will grant you superman strength and give you bubble shield that deflects all of the bad things in life. People always tell me that I can not get girls because of my attitude. Well thanks, you all just solved all of my girl problems.