Even if you could rule out man-made and weather-related causes for some UFOs, that wouldn't imply that they were caused by an extra-terrestrial civilization either. Some UFOs may still be unexplained, but all that means is that we don't know enough about them to say what they are.
That said, I don't think you can rule out weather and human craft. Others have already explained why I find the "primary" evidence unconvincing.
This is very speculative to me. I don't think we can use it as evidence for or against.
Let me put it this way. My guess of what an interstellar civilization would look like makes predictions about what it would be like to encounter that civilization. Those predictions are not satisfied. This is strong evidence that no extra-terrestrial civilization (as I understand the term) has made it anywhere near us.
One of the reasons you were downvoted is that you asked us to evaluate evidence for "Aliens". But that is impossible until you explain what you mean by "Aliens". Obviously, there is something about these UFO sightings that makes you think they are more likely to be caused by aliens than by weather. Which implies that you think you know something about aliens that makes them a better explanation.
So what is it that you think you know about these "Aliens"?
"Even if you could rule out man-made and weather-related causes for some UFOs, that wouldn't imply that they were caused by an extra-terrestrial civilization either."
I agree. But in the cases of grey beings emerging from UFOs we can at least conclude that grey beings can occupy UFOs, if we trust primary evidence. This would be a massive discovery in itself, so why don't we hear about it? We don't have to conclude they come from outer space - who knows, they maybe live underground. Lets not speculate on that as we have plenty of interesting observ...
Recently I've been struck with a belief in Aliens being present on this Earth. It happened after I watched this documenary (and subsequently several others). My feeling of belief is not particular interesting in itself - I could be lunatic or otherwise psychological dysfunctional. What I'm interested in knowing is to what extend other people, who consider themselves rationalists, feel belief in the existence of aliens on this earth, after watching this documentary. Is anyone willing to try and watch it and then report back?
Another question arising in this matter is how to treat evidence of extraordinary things. Should one require 'extraordinary evidence for extraordinary claims'? I somehow feel that this notion is misguided - it discriminates evidence prior to observation. That is not the right time to start discriminating. At most we should ascribe a prior probability of zero and then do some Bayesian updating to get a posterior. Hmm, if no one has seen a black swan and some bayesian thinking person then sees a black swan a) in the distance or b) up front, what will his a posterior probability of the existence of black swans then be?