Based on ZERO Evidence, of Course. Big Deal.
Anybody can make unsubstantiated claims of anything without the slightest proof. So what? I can claim that I once turned a pound of butter into gold, or that I have fairies living in my attic. Such claims are devoid of meaning, let alone validity.
Nobody has ever come up with a shred of evidence, not the tiniest iota, that Earth has ever been visited by extraterrestrial intelligence, recently or in the distant past.
Edgar Mitchell's unsupported beliefs are no more valid than those of anybody else. The fact that he was an astronaut is irrelevant.