Yeah, Warner was just protecting their IP. Not just because he made that ad as Joker, but because they don't want their characters used in endorsements for things like alcohol.
Which is crazy, when you think about it. Joker murders countless people in the movies, and in the comics is best known for incidents like beating a child to to death with a crowbar and leaving the body in an exploding building for Batman to find, and showing up at a woman's apartment, shooting her in the midsection to paralyze her, stripping her naked, taking suggestive photos of her, and then forcing her father to view said photos. But saying the character likes alcohol a real person can go buy? Nope, too far.
