BedouinLeo, I think si403 may be referring more to carbon offset companies rather than airline requesting paying customers to pay to offset the carbon.
Sure, buying carbon offsets is viewed by many as a (relatively easy) measure to assuage our guilt. A bit like a bribe to make the problem go away. I have heard someone said this - "Oh I've paid for some companies to set up measures that reduced carbon emission, and that will counter the carbon emitted from my travel so it all balances out."
That is, of course, defeating the purpose. Balancing out is not the goal here - it should be net total reduction of carbon emissions.
Nonetheless, for many, this is all of good intention because they really want to reduce the impact of their actions, while not giving up on something else that they love completely. This is the best compromise that they have right now, until a better solution comes along.
I don't know how successful the carbon offset companies are in achieving the goal in reducing carbon emission though, nor do I know how well they are managing their projects and handling the monies ethically. In setting up any projects, in short terms, there are high likelihood that more carbon is being emitted from the production, the transportation of project materials etc. In the long term, perhaps the benefits to be reaped greatly outweigh the setbacks currently seen. Nonetheless, the whole initiative is still new that an accurate measure is not possible at the moment.
[ Edit: Edited on 07-Nov-2009, at 02:51 by lil_lil ]