That's just dumb. It would be one thing if they were having a quiet conversation among themselves whispering back and forth and were told to stop. But clearly OP could hear them, they weren't being quiet. And allowing such behavior to go on where people can clearly hear it is the same thing as condoning it. That's besides the fact that if you're going to act like that during a talk, you shouldn't be in the room anyway because you're being a distraction to everybody else.
> allowing such behavior to go on where people can clearly hear it is the same thing as condoning it
Toleration is what allows people who have different views to work together toward common goals. You can't have civilization without it, because no two people will agree on everything. If these people were really as boorish as the OP described, the best approach would have been to let them embarrass themselves.
What's next, hushing someone who dares admit he voted for a Republican? (I can imagine the rationale now: "you're enabling war and bigotry by proxy! Public GOPism is unacceptable!")
The paradox of intolerance has been largely derided since the 1940s, and for good reason. If you do not confront and quell threats to your community, they only ever fester. They don't go away, they get worse--see GamerGate and the rest of the reactionaries happily SWATting female academics and game developers in the name of "ethics in games journalism," and how that didn't magically appear when Adam Baldwin put a name on it (but the name legitimized them and let them act openly, for a time, before everyone else caught up).
Allowing people to be sexist jerks (let's not dress it up as "boorish") doesn't just let them "embarrass" themselves, it creates an effect within a subculture that gives that activity preferential status because few people want to use their limited public credibility to counteract it--thereby over time letting sexist behavior become the expected norm of that subculture. That's not OK, and speaking up directly confronts the issue and prevents it from becoming a social norm, or becoming further entrenched because we live in a profoundly sexist society to begin with, in that subculture.
