Adam did his best to not harm anyone. It was his purpose on the team, after all. To keep everybody in one piece. He wasn't certain if he could bring himself to end someone's life period. It went against everything he believed. To him, the Legacy would always be about preventing loss of life.
Ian probably did too, but really, Adam didn't want to know what Ian did during his time off. "Could be a good idea," he agreed. "Of course, somebody'll have to stay on the island and make sure the kids don't destroy the place."