If there was a huge amount of evidence, it would be unjustified to reject the idea. But there isn’t. It’s possible to make a convincing case that there is evidence, but when you ask for the solid, unambiguous evidence (i.e. data that would be hard to fake), it’s just not there. And you would expect any civilization that is capable of interstellar travel to be able to remain undetected by humans if they wanted to, or if not, you would expect those with the best instruments to detect them first. Mile-across, fast moving objects should show up, not just on military radar, but also on Doppler radar (what they use for looking at rainfall). Fragments from a crash-landed spaceship should have a significantly different isotope ratio than alloys on Earth. For that matter, you would expect a highly advanced civilization to have done some interesting stuff with Carbon (nanotubes, etc), not for them to still be using Aluminum.
Basically, there are a bunch of things we would expect to see if there actually was a highly advanced civilization present and detectable. And we don’t see those things.
If there was a huge amount of evidence, it would be unjustified to reject the idea. But there isn’t. It’s possible to make a convincing case that there is evidence, but when you ask for the solid, unambiguous evidence (i.e. data that would be hard to fake), it’s just not there. And you would expect any civilization that is capable of interstellar travel to be able to remain undetected by humans if they wanted to, or if not, you would expect those with the best instruments to detect them first. Mile-across, fast moving objects should show up, not just on military radar, but also on Doppler radar (what they use for looking at rainfall). Fragments from a crash-landed spaceship should have a significantly different isotope ratio than alloys on Earth. For that matter, you would expect a highly advanced civilization to have done some interesting stuff with Carbon (nanotubes, etc), not for them to still be using Aluminum.
Basically, there are a bunch of things we would expect to see if there actually was a highly advanced civilization present and detectable. And we don’t see those things.