there was also no implication that she liked it and wanted to fuck him
Look, you can speculate as you like but without any evidence, stop calling Doflamingo a rapist.
Does Doflamingo have the heinous attitude to be a rapist? Sure. But he has not been portrayed as one. Plus, Oda didn't say that Doffy forced himself on Viola. Oda said of "passion". That doesn't equate to rape.
In any case, for all the evil Doffy has done, rape isn't shown to be one (and Oda isn't afraid of showing that, he basically showed that the CDs are rapists). Besides, He protected Baby 5 without any sexual benefits, didn't he?