Can we confidently dismiss the existence of near aliens? Probabilities and implications

An earlier post of mine reviewed the most credible evidence I have managed to find regarding seemingly anomalous UFOs. My aim in this post is to mostly set aside the purported UFO evidence and to instead explore whether we can justify placing an extremely low probability on the existence of near aliens, irrespective of the alleged UFO evidence. (By “near aliens”, I mean advanced aliens on or around Earth.)

Specifically, after getting some initial clarifications out of the way, I proceed to do...