Better count all the unmanned missions since Apollo that have gone to several planets, and completly out of our solar system. 130 Space Shuttle missions, Our Space Station, The Hubble Telescope. Don't think we are afraid of Aliens.
Greeny, None of these missions you mentioned were intent on setting up a permanent colony on another planet. I think what CodeBlack is saying is that the aliens are not happy with us sticking flags on other planets and claiming them as our own. I don't think they want us spreading tribal warfare though out the cosmos. And via the testimony of officials from the US Army, US Marines, US Navy, US Airforce, Nasa, Whitehouse, FAA, The British Ministry of Defense, British Police, French Military, French Aerospace industry, Boeing, Northrup, Honeywell, McDonald Douglas (to name a few) the notion that we were told in no certain terms to stay off the moon is a very real one.