A quote from Joey of the "Friends" TV show sums up the answer to this question for me: "It's like a cow's opinion. It doesn't matter. It's MOO." However you say it, the question is moot. Some people are ready and some are not; some believe and some don't believe. The real question is, are we ready for what will happen once they get here? But that question assumes everyone believes the same thing. So to further pare it down: Are YOU ready for what YOU believe will happen once they get here? And will that belief hold up in face of reality?
Imagine you turn on the TV tonight and find Katie Couric interviewing the Jolly Green Giant (he'd be hunkered down, I suppose). Do you feel "ready" for that? This isn't even a good example, because unlike aliens, the Jolly Green Giant is familiar to many of us and we believe him to be quite benevolent. But he's really big and green and real (you watch in fascination as he smiles at Katie, his teeth as big as Volkswagons), so we're thrown a little bit. We don't know what made him leave his green valley in the first place. We don't know what makes him mad, so we'd probably try to placate him by eating a lot of canned peas at every meal. In fact, the world consumption of canned and frozen vegetables would no doubt skyrocket.
Even if you did believe in the Giant prior to his actual arrival, coming face to face with him might make you 1) go bragging to your friends that you were right all along and not a crazy nutcase, and 2) jump for joy because something really interesting is going on that will change the world forever. And you run right over to the big guy to ask for his autograph.
Get in line. Because the government is there first, putting a fence around him and asking him his intentions. And the religious leaders are right behind the government, asking what (or who) he believes in. And based loosely on those answers, the media will tell you whether the Giant is a Good Guy or a Bad Guy. And you'll hope that the government is telling you the truth, because there's no way you were even going to get close enough to the Giant to actually speak to him. He's too scary-looking close up, anyway. And the religious leaders have determined that he doesn't have a soul, so we humans are superior to him in that regard and the Giant should be run out of town. The media tells us that he carries some toxin that makes his skin green and do we want to turn into green-skinned slaves for the Giant?
Now you hesitate, and put your autograph pen away. You are frightened. What do we know about this Giant, anyway? You're suddenly angry that he dared to upset our humble world. Then you find out he "accidentally" stepped on a few towns on his way over, and an eye-witness swears he saw the foot grinding them in for good measure. And if you thought the Giant was scary when he was smiling, just look at him now.
Suddenly there is talk of war and armies of Giants waiting in the green valley ready to squash us all. That thought leads to the realization that even if we knew where his green valley was, we don't know how to get there and even if we did, how do you fight an army of Giants? In addition, we have no idea how long he's visiting, or if he plans to stay and turn the entire earth into one huge green valley, sans people.
Are we ready for the Jolly Green Giant to be interviewed by Katie Couric? I might be, and you might be. But HE isn't and SHE isn't. And neither are THEY. But there he is anyway. Ready or not. You see what I mean?