Cont'd.
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Cap-and-trade, if properly run, should yield an internalisation price that correctly fully internalises the cost of the negative externality, and so makes the market clearing price indifferent to on that basis.
It is very elegant, in theory.
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Setting an arbitrary price is much simpler, but will almost certainly get the price wrong, (virtually always way, way, too low, given political lobbying, e.g., $50/ton = 10 cents/L is, for certain, less than 1/7 of what is required, given that the higher price in Europe is not getting the job done).  Every time the price is forced up, there is a political price to pay.  
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Even if the tax revenues are then poured down the drain, either of these mechanisms will tend to be beneficial, even if not optimal - as will proscriptive regulation.
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Re-cycling the revenues back into general revenues, or back to consumers will both achieve the more efficient effect of taking the burden of the externality off the rest of the economy.
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(Cont'd)