You'd think the Marines would get a hint after Luffy kicked everyone's asses all the way from East Blue to the end of the New World (and maybe even beyond, if he decides that taking on the World Government's capital Mariejois is necessary for his quest) to become the second Pirate King.
They kidnapped Nami didn't they. They just technically digged their own grave. S*** just got real. They will kill anybody who touches her. But the completed they just need Sanji and then nobody survive against the three even if it was just Luffy and Eddy they still wouldn't survive O o_O