A> friendly to humanity,
B> even a little bit similar to us in any way, or
C> open to communication.
And most UFO/aliens stuff requires at least one of the above to be true, if not multiples of them. If their technology was roughly similar to ours (so relativistic sub-light travel and such), the only reason they'd make the journey would be for resources. In which case, we're competition/threat and to be eliminated, not to mention they won't be able to hide that well. If their technology is superior enough to allow them to break the light speed barrier, it's worse. Not only can they attack us in ways we can't imagine, but they're also so far advanced that they couldn't see us as equals. At best, it would be like modern society discovering a stone-age tribe hidden in the Amazon. More likely, they'd see us the way we see monkeys.
If aliens come to the solar system, we're done. We'd have no chance whatsoever of fighting back. Movies which suggest otherwise all involve aliens that are mind-bogglingly stupid, too stupid to have invented the tech they used to get here. Any smart alien is going to realise simple truths, like the inevitability of planetary orbits. If they want us off the planet, they don't need to fly down here and start shooting, they just need to shove some Kuiper objects onto the right path and wait for them to fall onto the Earth, providing an extinction-level event that clears the planet for them. And we can't dodge the planet out of the way, nor can we strike back. Or even resist; even if we shoot the first one down, there's hundreds of thousands of those rocks out there, and it's not hard to shove them onto a path that will strike the Earth. We'll run out of resources before they do, particularly as they can pillage the outer planets while they're bombarding us.
The idea that they'd run around is saucers hiding from us and abducting farmers for probing? That's just people making stuff up, or experiencing things like sleep paralysis and not recognizing it or what it is.