[wladimir]

On the other hand, the potential damage of one mistaken "Reply to all" can be enormous, compared to a mistaken "Reply" which just adds some extra work.

[afterburner]

Usually true, but I've seen an errant "Reply" cause misunderstandings too (due to lack of communication rather than inappropriate communication).

You're courting disaster anyways by replying off a mass email chain to one person on it.