Jacob is the bad guy by Broda

Jacob is indeed the bad guy, here are my reasons:
(a)When he visited Kate as a kid and paid for here stolen box, he took away the chance for Kate to be punished for her crimes. This led her to a life as a criminal/fugitive.
(b)When he visited Sawyer as a boy, he helped him finish his letter. That letter kept him angry for his entire life.

(c)When he visited Sayid he distracted him so that Nadja could be killed.
(d)When he visited Jack he gave him the confidence to talk back at his father which led to Christian being fired and to his death in Australia. He also told him that everything can be fixed ("it just needed a little push") which led to Jacks obsession to fix things.
(e)When he visited Locke (yes, he woke him up, but) he told him that he was "sorry". Being pitied kept John angry.
(f)He told his nemesis "It only ends once". Endings are always a bad thing (even Happy Endings) because it means something (in this case, my guess, everything) stops.
(g)He lives under the statue of Taweret. Since Tawaret is female and the gender of a god always stays the same in mythology it is highly unlikely that Jacob is Tawaret. But Tawaret was married to Apep - the god of evil.
(h)This part is a little far-fetched but its a theory: I think Ilana might be Tawaret because he told her to help him, she knows about the significance of Lockes body and the question("What lies in the shadow of the statue)"). And because they kind of look alike.