I'd tolerate it, but not support it. Forcefully taking them away gains these platforms even more support and demand. Only when people seek for alternatives or a change on their own, we can solve the problems.
I don't consider that promotion. Think from the perspective of the people who happily use US big corpo social media. When you're forced to consume B, because A is banned, you're likely not giving B a fair chance, even if it would have otherwise convinced you.
(Obviously you must still enforce rules and ban the platforms that don't abide.)