Stephen Hawking thinks that it's a bad idea to contact alien civilizations:
Earth had better watch out, at least according to Stephen Hawking. He has suggested that extraterrestrials are almost certain to exist — but that instead of seeking them out, humanity should be doing all it that can to avoid any contact. …
He suggests that aliens might simply raid Earth for its resources and then move on: “We only have to look at ourselves to see how intelligent life might develop into something we wouldn’t want to meet. I imagine they might exist in massive ships, having used up all the resources from their home planet. Such advanced aliens would perhaps become nomads, looking to conquer and colonise whatever planets they can reach.”
He concludes that trying to make contact with alien races is “a little too risky”. He said: “If aliens ever visit us, I think the outcome would be much as when Christopher Columbus first landed in America, which didn’t turn out very well for the Native Americans.”
While I agree that any aliens reaching the stars are likely to be similar to humans or worse, meaning chauvinistic and rapacious but more technologically advanced, the problem is that we've been contacting alien civilizations since the 1920s through commercial radio, which bleeds off into space. The signals from Mexican border radio stations of the 1950s, designed to be heard loud and clear in Chicago and New York, are already introducing aliens to Buddy Holly and Little Richard, and will continue to do so forever.
And aliens can't dance. "Bob" help us all.