Whether there is life, and even intelligent life, somewhere besides Earth (insert intelligent life on Earth joke here) is not dependent on whether these craft are of alien origin. It seems that some people here think that if someone doesn't "believe" that these craft are alien spacecraft, then they don't "believe" in alien life, period. If these craft are built on Earth by modern humans, it doesn't prove that there isn't alien life out there.

I just prefer to follow the evidence to learn something, and not start from a belief and work backwards. So far, we have no reliable evidence of alien life anywhere else, and therefore, of course, no evidence that they have visited Earth. That does not prove that there is no alien life, or that they have not visited Earth, but seeing something we can't immediately explain is also not proof of either being true.