Zamasu hates mortals, he believes they should be eradicated. But since he’s a Supreme Kai in training that’s not acceptable. Gowasu, his mentor knows of this to some extent.

You only met him one other time. You went to his plant with the god of destruction, his attendant and your sayian friend from earth, Goku. Goku won a sparring match against Zamasu and it didn’t make him favor mortals anymore, obviously.