Intelligence as we commonly refer to it is not a given in evolution. Evolution seeks forward propagation of genetic material, it doesn't seek an "intelligent" state.
It's reasonable to assume there is life elsewhere in the universe. It's quite a bit more of a stretch to assume there is _intelligent_ life elsewhere in the universe, aside from the problem of defining what intelligence is.
There are an estimated 8.7 million species on earth. The common interpretation of intelligence puts the ratio of intelligent-to-non-intelligent species we know of at about 1:8,700,000. Nothing I've seen in the literature on evolution suggests that evolution will lead to intelligence under than definition. Mammals led to humans, and only after the dinosaurs were wiped out by a mass extinction event.
So while I can't say for sure that intelligent life is more or less common at a universal scale, it makes far more sense to assume the rest of the universe and the mechanics of evolution are consistent with what we see on Earth. I don't think we'd be that unique in the cosmos, which seems to me to be an egotistical thing to think, anyway.
Or maybe it happens all the time. But with only one sample, we have no data either way.
Sure we do, that one instance of life pushes the needle in favor of life. A fun exercise is to imagine or visualize the concept of nothingness, as far as you can take it. Eventually you realize even the "idea of nothingness" negates the meaning of "nothingness." You reach a paradox in awareness that you're incapable of resolving because to do so would mean the idea didn't exist in the first place. Applying it to life, the existence of life negates the existence of no-life, and increases the probability in our favor.
Functionally I think life is more commonplace than anyone realizes, and we're probably just incapable of understanding life outside of our perception of reality.
Given that life exists, here are two possibilities: life is common but we just haven't seen other life yet, or life is unique and necessarily we're it. Since those two possibilities look exactly the same to us, what data can we have to prefer either one?
If we ever did see other life, then we could be confident that it's everywhere. But without seeing it, we don't know. We can only guess, according to our personal preferences.
In fact, I'd go further. Compared to not looking at all, looking for life and not finding it increases the likelihood that we're alone. Maybe not by that much, since astronomy isn't all that good yet, but the more we look without finding, the more rare we'll know life to be.
Humans evince resistance to an obvious reality, we can't know what is unknowable, that is to say, that which we are incapable of experiencing. I can't know what another person experiences let alone some living entity built according to some alternate template.
Logic dictates a conclusion that other life likely exists in the universe. Also the odds favor that we can't know what it is given the intrinsic limits to what humans are capable of knowing.
But if you accept that the Dyson Swarms are a likely outcome then we have a while bunch of negative data points in systems within even thousands of light years of us.
That then brings into focus the hypothesis about Dyson Swarm. Such a thing can be built incrementally, requires no material stronger than stainless steel and requires no energy tech beyond solar power. It is a massive engineering challenge to be sure but not requiring new physics is significant.
But we have 4.543 billion years worth of evidence showing that life REALLY likes to live. To get from a single celled organism to me typing to you over the internet tells me there's probably something universal to this process.
To me it's a lot more "Main Character Syndrome" to suggest we are wholly unique and alone in the universe. We are the special chosen species that made it out of an infinite number of probabilities. Sounds insane.