SETI mathematical probability?

Is no good reason accept your umptions, "Drake equation" is just a string of umptions have no real basis, I read of several well-known men try use "Drake equation", their answers are 4000 - 400,000,000, is not real equation when have such great variations of answers when several celebrities try it, one is Carl Sagan whose figure is 1,000,000, when "Drake equation" have many unknowns we can only "guess-timate" it have no validity at real world, anyone caan pull figures out of a hat or his "ketsu' and do so well so use Drake's string of guesses, we not yet have enough knowledge even estimate simplest variables at "Drake equation", length of time communicating civilization last is debatable even at Earth, and we have no way know it at other planets, I think I can safely say probabalilty of SETI success at mission is REI (ZERO at Japan)!