...that violates board guidelines such as privacy, should everyone who participates in the thread be admonished or just the thread starter?

Sometimes people respond to the actual question without realizing that the poster has an agenda.

That's entirely possible, and it's also possible that the thread doesn't become inappropriate until further down in the thread. But I'm speaking of cases where the thread starts out, or very, very quickly becomes, inappropriate and members contribute to the thread in ways that continue to keep the thread inappropriate by continuing with and contributing to the inappropriate discussion. By inappropriate I mean break h.com rules.