re: I've seen these before, many times.
I do believe there are intelligent aliens on other worlds. And I think some of them are probably traveling through interstellar space. But it is a huge universe with vast distance between the stars. I have yet to see any concrete evidence any has visited us yet.
I do think that if they have find us (or when or if they ever find us), if they want us to know about them, we will. If they do not want us to know about them, we won’t because of their advance stealth technology. There shouldn’t be a gray area.
…unless they just don’t care if we know about them, but then, eventually, we would get some hard concrete evidence about them.