What difference does that make? I'm really not following you. When they sell, or buy, they pay the tax. It makes no difference if they place a limit order or a market order.
The spread is just the difference in prices, it's not an extra fee that some pay and some don't. The only reason it even exists is that where the prices meet trades happen, so the prices never actually meet for long.
The tax becomes part of the spread. The spread is paid (in aggregate) by the participants who take liquidity to participants who add liquidity.
It's not that market-makers and HFTs would not be assessed the tax at all, it is that they would be paid more than enough to cover the tax by the people who cross the spread.
The spread is just the difference in prices, it's not an extra fee that some pay and some don't. The only reason it even exists is that where the prices meet trades happen, so the prices never actually meet for long.