The most persuasive argument for the existence of Extra-Terrestrial Intelligent Life (that I know of) is the utterly chickenshit way its existence is being ever-so gradually, one damned, grudging extra-terrestrial planet at a time, admitted (by the Official Lizardly Admitters and Explainers of Things)--

"Otherwise," think these oh-so-gradualist, hierarchical, aristocratic Lézards-Explicateurs de Haute Crèche who speak for the others of their species, who own us, and exploit us, and, simply for their own comfort, don't want to think about a Galactic Civilization so barbarously and cataclysmically devolved that there were no 5-star restaurants in it serving Mexican toddlers à  la bave et au sang, "these wild-eyed anarchic, Luddite apes" (by whom they mean us) "will go rocketing off, bombing and breaking up the Eldest Great Lineage Egg-Clutches of their Nearest Interstellar Neighbours" (by which they mean themselves on the planets of Alpha Centaurii)--"And it will be the End of Galactic Civilization As We Know It." Flesh-Eating Lizards from Outer Space are always looking at the Big Picture, while at the same time dreading the loss of particular items from their Menu (which is representative to them of their by-themselves revered billion-year-old hyper-aristocratic Galactic Civilization)--rather like the French, whose Pâtés de Foie Gras de Dindon et de Canard hold the place, of cruelty and succulence, occupied among extraterrestrial lizards by toothsome Mexican tots.