Sorry to tell you, but there aren’t “take off slots” to GSP. Those only exist for the extremely busy airports and only at certain times. The pilots probably said that this happened to passenger shame and provoke the other passengers ire towards this person.
Getting up during taxi, takeoff, turbulence, and landing is dangerous for oneself and other passengers who you might fall on. However, if the choice was this or soil oneself, I can guess what I’d choose.