Is it that some of you completely disbelieve in the idea that aliens exist (at all) - or - are you open-minded to the possibility, but don't believe (are skeptical) they've ''visited'' Earth, yet? I'm in the latter group.
I have said many times that I'd be extremely disappointed if it turns out that there are no intelligent aliens out in the universe somewhere. With so many planets available, it seems very unlikely that life would only arise on one of them. (It would be nice to find life on Mars or somewhere, because if life started in two planets in the same solar system, then the chances will be very good indeed that life will be ubiquitous in our galaxy alone. Unless the life on Mars came from Earth, or vice versa, which is possible. But that's another story.)
On the other hand, it's very quiet out there. One would think that at least one intelligent species - if they exist - would have invested in a big radio transmitter to try contacting other civilisations. Mind you,
we have only been broadcasting weak signals into space for 100 years or so, so the "bubble" of radio noise that surrounds our own little planet is only 100 light years wide at the moment - a minuscule volume of space compared to the galaxy. There's only a smallish number of stars within 100 light years, and they are the only ones that could possibly receive our signals (unless somebody out there is constructing roaming probes, which is possible).
What we can say for sure about alien visitations to Earth is this:
if they are happening, then the aliens are doing a great job of hiding from us. So good a job, in fact, that there's currently no convincing evidence of alien contact available to us. On the other hand, it's far more likely that the aliens (if they exist at all) simply haven't visited us. Chances are good that they don't know we're here. Besides, interstellar travel is probably going to be
very difficult, however one tries to go about it. That's why making contact by radio makes a lot more sense, at least initially. Much cheaper to do it that way, and much easier to reach a wide audience.
Of course, I could be wrong. But it's totally
not up to me to prove that aliens aren't visiting us. It's up to the people who claim they have good evidence that aliens
are visiting us to present their evidence and argue their case. And just look at what a poor showing the True Believers are putting on for us, just in this thread on this forum!
One other thing: arguments from ignorance do not equal evidence. If you see a strange light in the sky that you can't identify, then the default conclusion is not "It must be an alien spaceship" (or, in Q-reeus's case, "It must be a paranormal ghost from another plane of existence", or whatever). If
you don't know what it is, then it's an unsolved mystery, for now. That's all. Get back to me when you
do know what it is, and when you can show me the evidence that strongly supports the conclusion that it's aliens, or paranormal time travellers, or magical pixies from the Forbidden Forest.
Think about this, too: UFO enthusiasts have had about
70 years now to dig up some good evidence of aliens (or whatever). But the vast majority of stuff they count as evidence consists of unreliable anecdotes, fuzzy photographs and pure fantastical speculation.