Visitation not impossible...
Just bloody difficult and expensive. Sure, aliens will have economics of some kind, just like us, why shouldn't "expense" be a barrier too?

As the late great Douglas Adams said: "Space is big. Really big. You just won't believe how vastly, hugely, mindboggling big it is. I mean, you may think it's a long way down the road to the chemist's, but that's just peanuts to space..."

The grasping of this fact may be why, on average, science fiction fans seem to be rather less likely to believe in actual alien visitation than the general populace.
( Amish Information Systems hates misplaced, commas, Mon 7 Jul 2008, 18:11, Reply)