'Open marriages' expect less of people. They are 'honest' at the cost of serving any coherent function in personal development or discipline. If you don't want to commit to at least attempting fidelity, don't get married.
I have to agree with you on that. If one wants multiple sexual partners, then don't get married - Unless of course the marriage is purely for business purposes ŕ la House Of Cards/Underwoods. Open marriages are not something the vast, vast majority of people could practice without significant conflict and ultimately, divorce.
Further, it's hard to see how most people wouldn't begin to form a bond and eventually feelings/love for their extramarital partners. Not necessarily every/any partner, but the chances are high it will happen to varying degrees - Especially for women. This alone should be reason enough to avoid such a thing. It's one thing to have sex, but another entirely to love.
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As for Bill - I think he was a good president in that, no matter what anyone thinks, helped the Democratic party regain/retain power in the face of a conservative political realignment and set the stage for a leftwards shift decades later. His personal life though... ew.