Well, an utter lack of evidence gives us reason not to accept such a proposal...That's what I think.There is no intelligent life elsewhere in the universe. The chances that some other planet would have all the required conditions for life are so remote as to be non-existent.
Because if the chance of sentient life was even 1 chance in 1 trillion, there would still be numerous advanced civilizations in the universe, and if there were, they would have explored Earth by now.
What makes you believe that they have not explored Earth?
I swam across a lake and left no evidence, does that mean I did not swim across the lake? Lack of evidence of an event is not evidence that the event did not occur.