I was watching the commentary for Sock Opera, and at the part where Bill tries to talk Mabel into handing over the journal, here’s what Alex says:

“Bill genuinely believes that Mabel is like him. He sees Mabel as a chaos agent. Mabel has a little bit of a seed of anarchy in her, she’s a little bit selfish, she likes to have fun at whatever cost… and Bill is all those things times a billion. So he thinks that when he lays it all out for her, like “HOW ‘BOUT INSTEAD OF BEING LAME, YOU DO SOMETHING FUN! AND CRUSH WHOEVER YOU WANT IN THE PROCESS!” … he thinks that’s gonna go over! And he’s not wrong in seeing that side of Mabel, but Mabel is a better person than Bill Cipher.”