It’s victim blaming. Would you say a victim of Stockholm Syndrome is “free to leave at any time”? No, because that’s a ridiculous argument. Would you say Snowden is “free to leave [Russia] at any time”? No!
So why is it an acceptable argument when it’s Assange? Because he possibly committed a crime in Sweden? Because he indiscriminately blew the whistle on the US government’s crimes?
Sure, he’s a puppet of Russia, but to say he doesn’t deserve the same protections as the rest of us is to argue for tyranny.