Don't think it's a dumb question at all... Their is ofren times in a relationship where one of the partners had a "Kink" that they liked and wanted to try and their partner accomodates and does not deny them exploring their fantasy/kink because ir makes them happy.
If I look at my own relationship and If you asked my wife who's fantasy (idea) was it for her to be a HOTWIFE and to sleep with other guys and she will tell you it was mine. She still jokes everytime she plays with other guys about "The things she has to do because she loves me" it's 100% my fantasy that we are pursuing. She just wins/scores by default.
I would say that 99.5% of the sexual things we have done have come from my side (I just know what she likes even if she doesn't, lol)
This question shouldn't be confused with the "So who wanted to start swinging" ? Question.
We have met allot of couples that were only playing because their partners wanted them to. In most cases it is usually the husband that pressures the wife into the Lifestyle because the want to shag other woman. So its not so much a fantasy anymore but a selfish personal desire, and they couldnt care less if their partners were ok about it. Most guys have only thought about them shagging someone elses wife but never thought about some other guy shagging their wife. Trust me These play dates always end in Tears (and it's the husband crying). Speaking from many experiences
If you are in the Lifestyle for the wrong reasons it will never be successful.