I think tptacek thinks in a way where he's giving you charity in an uneven discussion, so he's not obligated to go further; perhaps harsh, but his reputation warrants a little pause before simply saying "bullshit".
His reputation is specifically why I asked for a source. While I don't doubt he's an intelligent individual, I've noticed that he also likes to "shoot from the hip" without providing evidence of many claims he makes on both here and Twitter.
> Every year, the number of people and businesses that rely on email gets smaller --- in the last 5 years or so, by something like 15%.
Are you sure that's not just the spam decreasing?