I have heard this claim with respect to UFOs in every single decade from the 1960s on.

In the 1960s, 70s and 80s I kept an open mind and was hopeful. At some point, you have to become realistic.

Unexplained lights in the sky are nowhere near enough evidence to support this huge great theory - particularly when we know that the US and other militaristic nations have been experimenting with secret military for almost a century now. (I still remember my bitter disappointment when all those well-attested accounts of silent, triangular UFOs in West turned out actually to be the Stealth Bomber.)

Why would intelligent aliens play these stupid cat-and-mouse games for generations?

People hope for magical change because our actual prospects are so very dark and grim that a compassionate person yearns to believe that we will somehow be saved from the consequences of our actions.