To Horatio's point about human nature, I think Quark shows he has some insight into humans
"Let me tell you something about Hew-mons, nephew. They're a wonderful, friendly people – as long as their bellies are full and their holosuites are working. But take away their creature comforts... deprive them of food, sleep, sonic showers... put their lives in jeopardy over an extended period of time... and those same friendly, intelligent, wonderful people will become as nasty and violent as the most bloodthirsty Klingon. You don't believe me? Look at those faces, look at their eyes..."