You've completely misunderstood how sanctions work there. There are entire nations that use the US dollar as currency without obeying any such rule or suffering any consequence.Trillions of dollars of trade happens every year that US law has no jurisdiction over whatsoever.
In a strictly economic sense, an FTT is perverse, in that it has unwanted side effects. One such effect is to drive trading activity offshore. But others include reduced levels of trading, which reduces liquidity for the shares themselves and makes mispricing harder to spot, this affects smaller companies more than larger ones, which adds value to large companies at the expense of their smaller competitors.
Another is that it stands to achieve one of its objectives - to promote the long term ownership of shares - the wrong way. It doesn't make long-termism more rewarding by promoting better corporate governance, it simply scares off flighty capital which usually won't go to long term publicly listed equities.
Public listing for companies is already in the decline. This tax is a big hike for all the funds that trade a lot, but whatever shares you own, you do eventually want to sell to those guys. The opportunity won't disappear of course. Perhaps business as usual will still carry on - if so their capital costs will be higher so your gain will be lower. More likely though, they won't want to work that way any more, there are less rules and friction for Private Equity, so this risks pushing more capital that way.