He jumped at the opportunity to fight Tito Ortiz. Dana has the stones, that's not in question. Ortiz failed to show for their scheduled fight. Atencio is a 155 pounder. The commission would never allow the fight and if they did, we may see the UFC's first death inside the cage. Atencio is a very low level fighter. Have you seen his fight tape? From all accounts of people who actually know, Dana is pretty damn tough!
Your Mayweather example holds no water. First of all, it was Mayweather who was claiming to be able to KO Chuck Liddell and second of all, both Mayweather and Sherk are professional fighters, so it makes sense to seek a fight between the two of them.
Atencio has as much chance of beating Dana White, as you have of beating me.