In the interest of not taking this out of context, I will quote the paragraph the sentence appears in and simply bold the sentence in question.
"There's the `slippery slope' view that as soon as you start to do this research, you say it's OK to think about things you shouldn't be thinking about," said Steve Rayner, co-director of Oxford University's geoengineering program. Many geoengineering techniques they have thought about look either impractical or ineffective.
Painting rooftops white to reflect the sun's heat is a feeble gesture. Blanketing deserts with a reflective material is logistically challenging and a likely environmental threat. Launching giant mirrors into space orbit is exorbitantly expensive.
This is why scientists both rule and are sometimes considered ridiculous. They have actually considered and discussed launching giant mirrors into space in order to combat global warming. And the only reason listed for not going ahead with this plan was that it was too expensive. I'm betting their list of reasons for why they should do it including "Because it's fucking bad-ass man." and "It's totally what they would do in some ecological disaster movie like Day After Tomorrow or 2012."
I have to point out that some of the other ideas listed after that were quite good and you should read the rest of the article, but I am no scientist so I don't feel qualified to really commentate on the rest of the ideas. All I can say is that I knew I had to write this blog because when I read that one sentence I started laughing so hard that I nearly choked to death on my Starbuck's coffee.