Joseph Gordon-Levitt and Sophia Bush are among the Hollywood actors jumping to defend their involvement with billionaire investor Peter Thiel ‘s mysterious Dialog group, assuring fans that they do not know the controversial conservative political activist and that the meetings are not “a single ideological gathering.” The stars, including Josh Brolin , are responding to a list of attendees leaked to The Hollywood Reporter and published this week , revealing to the public their affiliation with the private and invite-only group that is linked to Thiel, the co-founder of data analytics firm Palantir Technologies and the man apparently behind the group, which invites powerbrokers across the world in politics, tech and media to discuss “off-the-record ideas” in privacy. Researcher Maia Arson Crimes provided THR with materials about the group, including a membership directory and details about this year’s upcoming forum.…