That's just science at work, and every theory has it's "difficulties" answering all of our questions. The fact that this particular wiki article has a "Difficulties" section doesn't disprove the scientific merit of the giant impact theory, it proves that the wiki writer tried to give a complete picture and wanted to list some of the interesting questions still out there. Simply put, the giant impact hypothesis has no rival that provides as many self consistent lines of reasoning right now.

Newton was just as petty and and seemed to have a *staggeringly* large ego, despite his famous quote you mention. You can get an idea of his craziness from his Wikipedia page, though to get a better idea just google around to see plenty of fun stories about Newton's interations with Leibnitz (Math), Hooke (Optics), and Flamsteed/Halley (Astronomy). I'm sure there are more I'm forgetting, too.