"The aim is to make people think before they stand up in front of an audience, and also to avoid lengthy and entirely pointless arguments about whether or not somebody's unhappiness is logically justifiable."
Hmmm, so the speaker must think about how he might offend people who are illogically unhappy? How is one supposed to figure this out by thinking? "Think hard about how illogical people might react?" Why is the speaker held to a higher standard than the audience? Or should I ask instead, why should the speaker lower himself to the standard of some minority in the audience? This is not a recipe for creating conferences which involve critical thinking, it is a recipe to create conferences which only talk about known agreed upon things; what a waste of a conference.
"Don't deliberately offend people, and if you accidentally do so then apologise and attempt to avoid further offense".
And what if I make an extremely important ethical point (not just some random joke) that accidentally offends some people, am I suppose to apologize because they hold unethical beliefs and were offended? I might be offended at their beliefs, should they apologize to me?! What if I am offended at your guidelines (I am), should you apologize to me? There is no end to this circular logic.
The reality of political correctness is that it is not about being offended, it is about which particular subjects one may or may not be offensive about!
* It's NOT OK to be offensive about race, sex or religion.
* It IS OK to be offensive by potentially advocating a particular political point: free software vs opens source, or that you may or may not (ethically) use proprietary software. It is OK to be offensive by telling people their software lacks important features or is buggy/insecure. It is OK to be offensive by ridiculing older not so well designed software. It is OK to be offensive by telling people that they didn't think before speaking. It is OK to be offensive by insulting large corporations at which many in the audience might work, by claiming that they do not contribute their share, or to speculate about the evil reasons they may have done something...
Political correctness is hypocritical agenda pushing which in itself should be viewed as offensive.