The first thing the faction did wrong was to tell Klaus he had to follow their rules. The worst thing they did was hurt Marcel because Klaus then went into protective parent mode and the look on his face said "FUCK WITH MY SON AND YOU FUCK WITH ME"
The thing I personally hate about this scene is that when they start shooting Klaus takes a bullet and falls to his knees. And I hate it for two reasons: 1) I know this is an area where the lore is quite inconsistent, but as originally introduced Klaus should not be too hurt by a wooden bullet. When Stefan shot wooden stakes into Elijah back when Elijah was first introduced, Elijah barely flinched. Originals should not be this vulnerable to wooden projectiles. 2) This is the more important reason. The thing about Klaus is that he often makes decisions where the consequences are negative but he doesn't end up paying for them. Instead everyone around him (be that his siblings or Marcel or humans or whoever) ends up getting stuck with the negative consequences. So wouldn't it have been extremely fitting (and also badass looking) if they shot up the bar, every other vampire went down and Klaus just stood there taking several wooden bullets to the chest and barely flinching? Klaus made the decision to snub the faction, everyone gets negative affected by it (hurt or killed by the bullets and the sunlight) except himself (who just stands there completely unhurt by either).
