I think that in verbal parley well-actually comments are a lesser degree of the same offense as shooting down someone else's idea in a brainstorming session. Not only does it tend to silence the first speaker by shaming, it tends to derail the larger conversation. In this written context, it's less of an issue, though nested comments do create a similar potential context.

Granted, sometimes you gotta break some eggs. But don't be surprised when the hen who laid that egg isn't to be happy about it.