"Selling out" is such an ugly term. Maybe Kantner lost sight for a while, but if he did, he redeemed himself later. I always thought it was pretty funny that he left and took the Jefferson name with him, the band continued as Starship, and Paul reformed The Jefferson Airplane. Anyway, you could call it selling out, but I think what he was doing was trying to keep his band alive. Popular music keeps changing, and Kantner wanted to keep writing meaningful music, but he also knew that it didn't mean much if no one heard it. That's why Jefferson Airplane and Jefferson Starship albums always had some radio-friendly singles in there with the meatier stuff.
After Paul bailed, it's no surprise that most of the rest of the original crew followed him, willingly or otherwise. Okay, Donny and Craig weren't original Airplane, but Craig was the longtime Jefferson Starship guitarist. Donny came on board later through Mickey. I hadn't heard why he left; I'm kinda surprised that he and Mickey had a falling out, since Mickey basically got him the gig (Donny was the drummer for the old Elvin Bishop band, of which Mickey was the lead singer).
Anyway, Starship was definitely a different band, a strictly commercial venture. There's nothing wrong with that; if your goal is to write hit singles and you do it well, more power to you. My only beef with them is that I always called The Jefferson Starship just "Starship" for short, and I couldn't do that anymore because they weren't the same band, and I didn't really like Starship.