I don't buy that excuse, myself. The DEA is not short on funds because they go out and bust smugglers and dealers whose money and possessions further finance DEA operations.
The same thing could apply in the stock market.
As a matter of fact, they might find additional funds if taxes from the increased taxable income from investors/traders (who were no longer filing near as many tax losses) were directed towards them (the SEC).
Also, I imagine these large Market Makers probably find ways to avoid heavy taxation, just like they avoid naked shorting laws, taxation that in the hands of the small investors/traders, would probably get paid.