The AC is right. You are just introducing a strawman into the argument. If you are going to argue the monetary costs of a fuel, then you really shouldn't introduce human-contrived externalities into the mix. The danger in doing so is that then you have to figure out where to draw the line. Because whose to say that wind and solar don't have their own problems that are centuries in the making, as well? Oh, say like the future scarcity of silicon from manufacturing solar panels, or impact to migratory birds from windmills.
I am exaggerating the impacts from solar and wind here, but the point is that if you are going to insist on including the costs of CO2 emissions into the subsidization equation, then you also should include the future environmental costs of the other "green" methods as well. And the trick here is that it is really hard, if not impossible, to predict how future generations are going to place value on aspects of these technologies that are currently not seen as having a societal cost.
The only reason you want to account for the costs of CO2 emissions is because you, along with many other humans, are placing a (negative) value on that. I am sure there are Eskimos living in Alaska that would place a positive value on a warmer climate. Shouldn't you attempt to include their feelings in the matter? Why is your opinion and valuation more important than the Eskimo's? Whose to say the world wouldn't be an overall better place to live a few degrees warmer? Maybe we should be charging more for wind and solar because they ultimately would be preventing us from reaching such a panacea?
Far better to just avoid playing these "what if" games.