"Casting nasturtiums" - a popular, intentional malapropism for "casting aspersions" frequently used for comic effect. The effect is somewhat limited if the reader doesn't know that.
As for unnecessary - I think suggesting that the people who prefer the secret stay secret are doing so because they want to get away with sending something that's taken less time or effort or will be somehow embarrassing when revealed is *definitely* unnecessary. Not extreme, just unnecessary.