Mark Ruffalo reveals Hollywood stars are 'scared': Here's why

Mark Ruffalo is a voice of conscience in Hollywood. From matters of human rights to speaking out against corporate consolidation, he is there.

In yet another example of standing up for causes the Academy-nominated actor believes in, he co-wrote an op-ed in the New York Times.

In a fiery piece, he lashed the Paramount–Warner Bros. merger but shared an unknown titbit.

Several Hollywood stars oppose the merger but are afraid to speak publicly.

“The most revealing thing about that letter wasn’t the people who signed. It was the people who didn’t," the Marvel star and American Economic Liberties Project research director Matt Stoller wrote.

"Not because they disagreed — because they were afraid. There are many reasons to block this deal, but we now believe the most fundamental one is what we encountered when asking artists to use their voices: fear. A deep, ugly and pervasive fear of speaking out.”

Ruffalo's piece comes after he signed, along with over 4,000 others, a petition calling for blocking the Paramount-Warner Bros. merger, citing job cuts and reduced competition from combining several companies under one umbrella.