Why Should Anyone Shut Up?

I post the odd comment on some public blogs where dwell a sizable number of AGW deniers, and recently one asked me the question, paraphrased, you do all these heavy carbon footprint activities, why don't you shut up until your own house is in order? He thinks I am passing the blame for the climate problem onto him and I can see he won't accept that, he even denies there is a problem -- can't say that I blame him. I read somewhere how to rephrase this so that it sounds better and perhaps an agreement can be reached. And that is: None of us are to blame for AGW, after all, the industrial revolution with its CO2 emissions began about 200 years ago, which greased the skids for today's situation. However, we all are responsible to do our part to clean up the mess. Those of us who are not scientists, like myself, can at least sound the alarm and try to convince our many ambivalent acquaintances. No good solutions will be possible without a strong realization the problem exists.