Gladwell doesn't go into detail in this piece about what he means by holding ideas loosely, but there's probably an important distinction between (i) loose in the sense that he's open to new evidence, and (ii) loose in the sense that his understanding is not deep.
Gladwell's performance in the Munk debate versus Taibbi et al. illustrates that when you're in (ii), it's often hard to defend one's ideas. He came to the debate expecting to get by on platitudes, and then pivoted to some ad-hominems rather than being able to defend the merits of his ideas. Based on post-debate audience feedback, it ended up being one of the most lopsided losses in Munk debate history.
Gladwell's performance in the Munk debate versus Taibbi et al. illustrates that when you're in (ii), it's often hard to defend one's ideas. He came to the debate expecting to get by on platitudes, and then pivoted to some ad-hominems rather than being able to defend the merits of his ideas. Based on post-debate audience feedback, it ended up being one of the most lopsided losses in Munk debate history.