Travel to those countries? The precedent here is that China has the right to extradite me for supporting democracy in Hong Kong from here in the U.S., never once even leaving my house. Assange was not a U.S. citizen, and located outside of U.S. territory.
Of course, the U.S. won't cooperate with the extradition request, but that's just a matter of power relationships, not principles. The principle is that everybody in the world is subject to every country's laws. Or, every person in the world is subject to the laws of the U.S., which fundamentally breaks the rule of law.
It's scary how many people out there are okay with that.