[fiblye]

That comes with the big assumption that in basically any given corner of the universe, civilizations in galaxies billions of light years away are pumping out radio signals strong enough to be detected from earth.

How likely is it that by the time humanity would be a space faring society that we’d be pumping turbo charged radio signals that are easily distinguished from noise when doing a quick sweep? How likely is it that societies are using radio signals or something similar for a long period of time, and not simply using some better method that humans have yet to discover?

[sailingparrot]

No, the assumption is because our solar system and earth are not particularly old, if life is commonplace, then there are civilizations that should be billions of years older than us. Imagine where we would be (assuming we don't simply destroy ourselves in the next 50 years) with a billion more year of technological progress? We should be all over the galaxy, colonizing left and right, sending probes everywhere, creating dyson sphere like structures that would be easily detectable from afar etc. And that is just one civilization on an single planet out of 100 billions planets in our galaxy.

Of course everything is just speculation, for every hypothesis on one side of the argument you can find 2 hypothesis from the other side that counter it. But the point is, to go back to the original question, that the right answer is definitely not obvious and if someone's opinion is that we are alone, or at least that life is very rare, it's not completly crazy.