"People who don't like the idea of gay characters appearing in fairy stories should think what they would think if they were gay themselves and why should they be excluded?" McKellen told CNN at the film's New York premiere Monday.
Actor Josh Gad's character in the film, LeFou, briefly dances with another male character at the end of the movie. The moment prompted Russia to restrict children under 16 from seeing "Beauty and the Beast" and one drive-in-theater in Alabama not to screen it.
But McKellen, who plays Cogsworth in the movie, said the scene is not "revolutionary."
"For people to complain about it and say they don't want children to see it is absolute rubbish," McKellen said. "I know people who don't like gay people and make a fuss. It's a very small moment in the movie, no one should get too excited."
Audra McDonald, who plays the wardrobe in "Beauty and the Beast," said the movie is about acceptance.
"There's all kinds of diversity within the world and we have it in this film," McDonald told CNN. "In the end, the film is about seeing past anyone's surface and looking on the inside. It's not only about learning to love someone else, but it's about learning to love yourself -- and that's deeply human, and we all feel that no matter who we are or who we love."
Dan Stevens, who plays Beast, told CNN he is proud to be part of the film.
"Like all great Disney films and all great movie musicals, it's in glorious technicolor and it really embraces all colors of the rainbow," Stevens said.
"Beauty and the Beast" releases in 4,000 theaters nationwide on Friday.