You've answered your own question. Terrorist organizations wouldn't use a public platform just like how they don't currently have recruitment booths in Times Sq

You've answered your own question. Terrorist organizations wouldn't use a public platform just like how they don't currently have recruitment booths in Times Square. If there are privacy implications those would be handled by legislature and judicial oversight like the rest of our public infrastructure. I don't see why a public platform for social media would need any sort of real life identify verification. Instead of having a private company decide who gets to say what, we have public representatives handle the curation. The FCC has been regulating TV and radio for many decades and as far as I can tell it is still relatively easy to criticize the government over public airwaves.