User blog comment:JustSomeDude.../790 & 791 - Break/@comment-21119641-20150628163108/@comment-5398287-20150630043131

I don't think you can really compare Viola and Robin, at least in that regard. Viola ALWAYS hated Doflamingo, and only joined his crew so that her father's life would be spared. Robin, on the other hand, was previously on the move from gang to gang for the protection each offered, and Crocodile extended that same protection (with him desiring her ability to read Poneglyphs), so she joined his crew. On top of that, Robin didn't want to kill Crocodile all along; sure, she may have lied to him in the endgame about the contents of the Alabasta Poneglyph, but she was quite complacent in his plans up until that point.

Vivi is far more similar to Viola, right down to the nobility aspect.