Villain or victem lashing out to fight for rights, it's still too strong of a conotation. Especially with the other meanings and uses Shylock gained after the play debuted. Just because a name belongs to a fictional character doesn't mean that it doesn't get a strong image with it. Romeo and Juliet are star crossed lovers, even if they're dating someone else. Voldemort is hatred and racism personified. Hamelet can't make up his mind.
http://en.wikipedia.org/wiki/Shylock