So are there any TLDs that are safe from seizure? If so, which ones? If not, which ones are less likely to be seized?
However, I could see a seizure of a domain in a different country's TLD (ccTLD to be specific) causing a diplomatic scuffle between the US and the foreign country. I can't imagine France would be thrilled with the FBI seizing 'foo.co.fr' or something.
.is, however, is managed by Iceland. Iceland has been positioning itself as a haven for organizations concerned about free-speech and broad-sweeping censorship.