Reminds me of this:

"This hacker guessed a password for their Unix system. From there, he became super-user by planting an egg in the systems area, then sliding into my computer.

A couple days later the SOB called me. Said his name was Dave. From Australia.

"I broke in to show that your security isn't very good."

"But I don't want to secure my computer," I replied. "I trust other astronomers."

Dave had other reasons for breaking in, too. "You think that hackers are bad. This proves otherwise."

"Huh? You break into my computer to show that hackers are good?"

"Yeah," Dave replied. "We're helping you out by finding your security faults."

Clifford Stoll, The Cuckoo's Egg

Would you consider the NSA to be doing the world a favor as well then?

Likewise asteroids are doing the world a favor by reminding us that an impact event could end life as we know it.