It's yet another socialist "get back and those who have" tactic.
There's nothing to agree to here. It is universally bad. This is triple taxation. I am taxed at my normal income rate on the money I put in (and so are the wealthy - that money was at one point taxed). Now, the tax man is coming to get their cut on a trade (both sides!), and then AGAIN when I close/adjust/etc.
This is highway robbery designed to pander to broke millennials too stupid to understand and too broke to think 10 years in the future.
We will probably see a dramatic drop in liquidity as people flee to safer instruments and/or move money into foreign exchanges to trade there (probably what I'd do, personally).