One truck delivering 30 bikes to the LBS (i.e. 1 bike = 1/30 truck) and only requiring that once every 4 years or something...
Driving on your own in a massive car 30 miles a day 300+ days a year...
...slight difference me thinks.

Of course we can not stop emitting carbon, we breath out carbon dioxide, even if we die our rotting corpses would emit some nasties, or you would be cremated. Cycling makes you breath harder so you give off less carbon sitting on the sofa.

Yes ok, I still have hot showers and cook my food before eating it, etc, but I changed my electricity supplier to a wind-farm-only company (do those even exist in the US?). I live in a modern flat that is highly insulated with modern efficient appliances. I use a laptop computer rather than a desktop and I don't have a tv, watching tv on my laptop. I don't use airplanes, but then that makes holidays much more interesting (went to hotel 200m down the road with my wife and all our friends thought we were so original and exciting).

Just because you can not elimitate your carbon emisions completly is no excuse for not at least trying to make a difference. That is like driving towards a brick wall at 50mph, then thinking that since you don't have time to stop completely, it is not worth using the brake at all... hmm maybe that is getting too close to the brakes/no brakes debate.