The evidence keeps piling up that life isn’t there, especially in our own backyard. (Even here on life friendly Earth the ratio of biomass to mass is one part in ten billion.) And with technology that allows us to see beyond our Solar System, the evidence is much better now than when Fermi made his famous observation.
But the most compelling evidence is the study of the tree of life. The probabilities for the events that led to us are extremely low. There was only one common ancestor that evolved around a hydrothermal vent. Mitochondria only happened once. Chloroplasts only happened once. All of those developments only happened once in billions of years. The fact there is only one tree of life is excellent evidence that life like us is exceedingly rare, and it’s dependent on the same physics and chemistry that exists everywhere in the universe.
All ET proponents have is the alien in the gaps of our knowledge and the gaps keep getting smaller.
As I said before, humans have only begun taking the first few tentative steps outside their local environment, and have barely scratched the surface of those few worlds we’ve visited or probed.
In time, we could find that only one planetary system in a million hosts life. Given the incalculable number of planetary systems in the universe, life would still prove to be abundant.
Naturally, this is all speculation on our part, but the probabilities involved argue for the existence of life elsewhere.
We are alone.