Your point is valid but keep in mind: Thailand charges no income tax at all on the profit from selling SET-listed equities, no matter how long they were held. If you are American, you will pay the capital gains tax to the IRS instead of Thailand's Dept. of Revenue.
In the U.S. there are transaction fees but they are so low that the big brokers offer free trades and absorb the fees. It's the U.S. income tax, especially on short-term gains, that hurts, even though long term gets special treatment at 15%.
I'd say don't sweat it. Announcements like this are intended to provoke pushback. By the time the fees are enacted, the rates will be less than half of those currently proposed.