For me, the argument about whether or not aliens exist, has been settled. The number of stars, planets and habitable zones, is just too vast for them not to exist. But I do think there is still debate about whether or not they have been to earth. I love watching shows like ancient aliens and speculating about how they might have come here, but as of right now, I'm still not convinced. It just seems that, if they had come here, the evidence would be too obvious to ignore, as opposed to the little tidbits that take large leaps of the imagination to connect. If aliens do have the technology to come here, my guess is that they've ignored us because we aren't a threat. I think it was likened to a colony of ants in a rainforest. Us, as humans, aren't aware of the remote colony of ants and since they aren't posing a threat, we have no reason to seek them out. I suspect, if aliens can travel through space, that's probably why we haven't seen any; we're just too insignificant for them to care about.