Between Bella and Edward, their flaws made the plot for Eclipse. Edward with his overreactions and Bella with her lack of self knowledge.
If Bella had known she loved Jacob and if Edward had not overreacted and been more honest with Bella by telling her how he felt about Jacob (he was jealous and thus insecure), Eclipse would probably be my favourite. Yet, alas, the characters kept their secrets from each other and in certain cases from themselves.
If Edward had been honest with Bella, maybe she would've understood she loved Jacob, and it would have solved a lot of problems quicker.
They both had issues. I think the only person who didn't in that triangle was Jacob. (oh wow. I never thought I'd say that.)
The only thing Jacob did wrong was that he went about trying to prove that Bella loved him in the wrong way, and you can't be angry with him for trying since he did truly love her and cares about her and thus is afraid Edward will kill her (sad that Edward can over come his fear of Bella and werewolves, yet Jacob can't over come his fear of Bella and vampires).
Although he probably should have understood better that one day he may imprint and hurt Bella, he was blinded by that adoration for Bella. Had Jacob used better techniques, she may have gone with him, which for us Edwardians would've been bad, and so I'm not as angry for he attempt date rape (again! wow!) since it meant Bella was ticked at him along with team Edward.
Therefore, Jacob kissing Bella was a good thing.