Why are they protesting specifically against Yoo Hae-jin??

I haven't seen the movie,
and I don't even know what kind of role Yoo Hae-jin plays.
I heard the cast is very impressive, including Park Hae-il, Lee Min-ho, Yoo Hae-jin, and other cameos.
Out of so many actors, why was Yoo Hae-jin targeted??
From someone who doesn't know much,
I wonder if it's because he appears on variety shows and has the most familiar image,
or to put it bluntly, if it's because he seems like an easy target. What do you all think??
They could demand an apology, but
I'm curious why they are going as far as protesting in front of Yoo Hae-jin's house.