Why do sceptics and atheists always offer ridicule instead of proof?

I've been on tons of questions here on Yahoo! Answers and have noticed how sceptics and atheists alike share one thing in common: They never have a solid backbone of proof or evidence. They always laugh at you and make fun of your own believes. In fact, the go as far as to put you down for believing in something they consider b**l s**t. Why is that? If their belief is true, valid, and correct; why don't they hand over the proof? Why do they always have to cut others down who don't follow in suit with them?