The Dr. Kildare actor was in the closet himself for most of his acting career, until he wrote openly about his sexuality in his 2003 autobiography Shattered Love.
Speaking to gay magazine The Advocate, Chamberlain said: "There's still a tremendous amount of homophobia in our culture.
"For an actor to be working [at all] is a kind of miracle, because most actors aren't."
He added: "So it's just silly for a working actor to say, 'Oh, I don't care if anybody knows I'm gay' - especially if you're a leading man.
"Personally, I wouldn't advise a gay leading man-type actor to come out."
Reports about his sexual orientation had been surfacing in the media for years but Chamberlain always refused to discuss them.
The 76-year-old Brothers and Sisters actor said: "Despite all the wonderful advances that have been made, it's still dangerous for an actor to talk about that in our extremely misguided culture.
"Look at what happened in California with Proposition 8. Please, don't pretend that we're suddenly all wonderfully, blissfully accepted."