No one denies that humans are still very much in the dark regarding many things. Also, no one completely denies the existence of certain apparently "supernatural" incidents. Even the most staunch atheists like Richard Dawkins say that if God-presumably, this encompasses anything supernatural-were to appear and present him/her/itself to them and give undeniable proof of his/her/its existence, then even he (Richard Dawkins) could no longer deny the existence of God. All scientists desire is undeniable-or as close to it as possible-proof of the existence of many of these things. With the scientific method being what it is, it is understandable that they would require this.