Simple, to quote the Joker: "All it takes is one bad day to reduce the sanest man alive to lunacy.
That is how far the world is from where I am. One Bad Day."- The Joker
He may not seem all as much for the Venom look, but it's all about power of actor to bring it to the big screen. Brought upon the character. That's what makes Venom or any villain, anyone period. It's all in the actor; you just gotta believe he/she in general could be great.