God help the universe!
The question is, what will we do when we find one? And it IS a case of when, not if. Believing that the Earth is the only planet of its type in the Universe is as logically absurd as believing that the Earth is the centre of the Universe. The same physical processes and laws that gave rise to the Earth also operate everywhere else, and while the conditions won't be right in every star system, there is no valid reason to suppose that stars like Sol with similar systems should not have life-bearing planets.
So, supposing we find an Earthlike planet orbiting say, Tau Ceti, Beta Hydri or Epsilon Eridani - all stars close to Sol in distance, size, mass and spectral class? Will that drive us to international cooperation in the development of a starship, or at least a robot probe? With the advent of quantum entanglement soon to eliminate the time-lag associated with long-distance communications, the only problem remaining is the seemingly insuperable c-barrier, and the energy cost in getting a vessel up to that speed. Perhaps with international cooperation and the world's finest minds attacking the problem, this may well be overcome.
Yet "Earthlike" does not necessarily mean "life-bearing". And "life-bearing" does not necessarily mean "intelligence-bearing". In fact, if we go by the Earth, in 4.5 billion years of existence Earth has fielded intelligent life for less than one five-thousandth of that time. And our civilisation has only advanced beyond horses, swords and sailing ships for less than one hundred-millionth of that time. So, given that all these planets will be in differing stages of development, the odds of finding a civilisation contemporaneously paralleling ours are in the millions-to-one against category.
So what when we do find a planet, we go there, and we find no intelligent life? Do we colonise, and destroy any chance the planet might have of evolving its own intelligent life? What if there is a civilisation still in its own Stone Age? Do we go there as gods and "educate" them - or more likely, enslave them? What if, against all odds, there is a civilisation like ours, that thinks that its way is right and ours is wrong - just as we think? Given the competitive behaviour of life in general, peaceful coexistence is orders of magnitude more unlikely than contemporaneous existence. Given human nature, I hold categorically that peaceful coexistence with any other civilisation would be absolutely impossible. Any ambassadors to the stars would be chosen by, and representative of, our greedy and exploitative ruling classes, and the outcome of any contact resulting from that is a foregone conclusion. Even if there is no intelligence, consider this: we can't take care of the only planet we have. What chance is there that we'll have any respect at all for another one?
All things considered, we should be leaving well enough alone. I seriously hope this Kepler mission fails to turn up anything. Not only for our sake. For the Universe's as well.