The solution to bad comments is deleting them before they are even visible to other users. Deleting aggressively, as is done in certain subreddits (r/science) may seem offensive towards naive users who just want to add their "2 c" to the discussion, but it's the only effective AND honest strategy: if your comment adds little of interest, it's worth nothing. The bar should be very high, the more popular the website the higher the required quality. But in the end I think NPR are making the right choice. Comments on websites are not a constitutional right, after all.