You can held them accountable the same way you held your junior developer accountable: it was a mistake, and they definitely could have done a lot better. Any blame wouldn't be unjustified. But what's the point and to what end?

Edit: the point is that it's missing the root cause. People could always be better, smarter, doing the right thing, be omniscience. But most of us are not. Between a rock and a hard place... there is no good choice. For all they know, all of their other 47 speakers are not speaking in the alternative case.