Canwest News Service: Liberal MPs say the Conservative government is attempting to stigmatize a potential Liberal proposal for a national carbon tax as “a tax grab” before the Liberals even finalize and announce their plan. Whatever design the Liberals choose, it will be revenue neutral, ensuring that taxpayers get back through reduced income taxes as much as they are charged in extra levies on fuel, Liberal finance critic John McCallum said Thursday. “By definition, something that is …