First you are 100% sure and then you start talking about possibilities? What do you know about impossibilities. You are 100% sure of something that isn't 100% a fact yet. You should not be trusted. Either step on the "im 90% sure" train and change your attitude or get labelled as a scientologist. It's as simple as that, science is not about claiming the truth, it's about keeping track of possible theories.

The universe is big, but if the creation of life is based on coincidence, such as the theory of the primordial soup, then the possibility that there are no other planets with life than earth exists. If life is created on lawful theories on the other hand, then the possibility that no other planet with alien life exists is virtually none (though quantum mechanics imply that everything is possible anyway). Many scientists believe in a hybrid of the two, however.

And this is only about primitive living cells, let alone intelligent life. You know the universe gets awfully lot smaller when you remember that life needs a lot of time to develop. There may be primitive life, but for a UFO to fly to our planet takes billion of years of evolution. And the universe is only 13.7 billion years old. That said the universe may be big, but there are no infinite star systems around. There's a big part that's got totally nothing. Our radial signals have come a long way, but we never received an answer back yet.

The search for intelligent life beyond this planet is a long one, and whoever finds it first, will immediately make this known to the world. NASA aint the only one aiming for space, and I sincerely doubt they let the chance slip through their fingers to report alien life before ESA or Japan do it for them.

And about cropcircles. A cute quote from The Prestige, and quite an accurate one:
"Now you're looking for the secret... but you won't find it, because of course you're not really looking. You don't really want to know. You want to be fooled."

Aliens are bad entertainers, as they keep leaving out the prestige.