Mankind has always been driven by contradictory drives. The relentless curiosity that pushes us forward and is directly responsible for our progress from caves to cities. The fear of change that tells us "hang on, these caves/cities are really nice, we don't want to risk losing them." There isn't any greater potential threat to the status quo than the discovery of extraterrestrial life, which is why some people would prefer we didn't try.
There has been some outrage recently over attempts to contact intelligent aliens, where instead of hiding in the corner and listening real hard some astronomers beamed intense directional messages up up and away. Critics decried these actions as dangerous, though their fears reveal more about us than any eventual ETs. They assume that they would be similar to humanity, so their first response to finding a more primitive culture would be to exploit the hell out of it. While such a fate might be pleasingly ironic (for anyone who isn't human, at least), others contend that any species that can make the journey here has advanced to a point where their goals are rather higher-minded than "Shoot us".
Dr Alexander Zaitzev, of the Institute of Radio Engineering and Electronics at the Russian Academy of Sciences, doesn't think much of these worries either way. A proponent of METI (Messaging to Extra-Terrestrial Intelligence), in a recent paper he shows that the odds of one of the METI messages being detected is a millionth of that due to powerful radar pulses regularly used in astronomical investigation. Though whether writing a paper saying "This METI thing we're doing has only a tiny chance of working" is overall a good idea remains to be seen. An important point is that METI represents an intentional will to make contact, rather than the accidental alien interception of some random radiation from Earth - the difference between saying "Hello!" and just being a suspicious strange noise late at night.
Most of the objections to contacting aliens are weak under close examination. We can't suddenly decide to hide after fifty years of pumping electromagnetic radiation into space without rhyme or reason - in fact, we'd better hope that an advanced civilization doesn't catch an episode of "American Idol" and just vaporize us outright. Suddenly keeping quiet would be like a drunk boyfriend carefully taking off his shoes after knocking over a bookshelf on his way to the bedroom.
Then there's the assumption that aliens would have the same kind of technology we do - despite the extremely obvious fact that our technology can't actually get to other planets. Any attempt to mask radio emissions will likely look like cavemen closing their eyes to hide from satellite imaging.
The simple fact is that certain people have always opposed progress while other, better people have driven it. "Experts" decried boiled water as unhealthy compared the vital stuff straight from the river, cursed antibiotics as a temporary placebo, and confidently declared that computers were nothing but expensive toys. As an intelligent species we must make every effort to contact anyone or thing we can - and if you don't like it, there are some lovely caves you can move back to.