This is actually a good point. Until we find proof of intelligent life elsewhere in our galaxy (or the universe), we cannot automatically assume it exists.
Don't encourage them, logician. We use statistics all the time as credible evidence for our activities. Medicinal trials don't actually prove that placebo effects (or spontaneous remission) are not responsible for "curing" a condition; they do, however, provide solid statistical evidence that a certain medicine was responsible (as in the chances of placebo being able to account for the change in condition amongst all participants would be a billion to one or something like that).
The notion that there are no other intelligent life forms in the
WHOLE universe is preposterous. There are billions of other galaxies
that we know about... The chances that earth is the only planet within the only star system within the only galaxy to contain intelligent life is beyond the realm of believability.
The question of whether intelligent life is near enough to us to actually contact us, or has contacted us... is another deal altogether. We should not presume that space aliens are nearby without evidence. I think it a bit presumptuous to assume that our planet has not been at least visited by other beings (once you consider multi-dimensionality a truth in reality), but we may not be currently being visited by aliens. That is something we should reserve judgment on.
MTF