Oscar-winning screenwriter Dustin Lance Black says he has no respect for actors who lie about their sexuality.
The US film-maker - who is engaged to Olympic diver Tom Daley - said people who mislead the public about their sexual orientation send a "negative message".
He told Attitude magazine: "I have no respect for someone who lies about their sexuality.
"At the very least say 'no comment', just keep your personal life personal. But if you're going to closet yourself, that sends a negative message."
Dustin said he blames Hollywood agents for making actors feel as if their sexuality will affect their career.
"I've never encountered homophobia in casting from the studios or networks, not once, not ever," said the 42-year-old.
"Where you encounter it is with the agents and the managers, they're the ones who have an outdated notion of the price an actor might pay if it's discovered that they're LGBTQ.
"Often they don't want to see anything happen that might compromise their investment."
He added: "I think they cripple their actors because they stunt the star's ability to be open and honest, and an audience can feel that."
The writer-director won an Oscar for his script for the 2008 film Milk, about the first openly gay man elected to public office in California.
His new drama series, When We Rise, dramatises the LGBTQ rights movement across several decades.
Dustin hopes it encourages more people to fight for equality, particularly in light of the recent US presidential election.
"I hope to inspire a new generation to stand up and fight back and protect what we have in a moment of darkness like this," he said.
Dustin has been in a relationship with Tom, 22, since 2013.
That year, Tom posted a video to YouTube to announce he was dating a man.
He said: "Come spring this year, my life changed massively when I met someone and it made me feel so happy, so safe and everything just feels great. And that someone is a guy."