So I can have an opinion on what is and isn't acceptable to say, in my home or in public. I just can't tell you what my opinion is?
I would have thought that JohnK is saying he is the arbiter of what he should or should not say in his house, but I don't read in that response that he is saying what you could say in yours, only that whatever others say his opinion us unlikely to change (which I must say is the default position of most people I know who have stood by their opinions for most of their lives).
I am sure most of us when we visit someone that we generally tend to be on our best behaviour and look for signs as to how we should behave to ensure we do not offend our host(s) by pushing our different opinions unless openly invited to do so (which was a very common feature in the '60s where no party was considered successful unless a decent conflict of opinion had been expressed over music, war, sex, drugs, politics etc).
My family makes lots of jokes about our shared heritage (Aboriginal, Cornish (not to be confused with English), German/Russian, Portuguese and a few other bits thrown in). We have developed a shared understanding of those limits and no doubt say things that others outside our group might find offensive taken out of our family context but are accepted within the group as humorous repartee. Those limits I would suggest are infinitely variable depending on the circumstances and individuals involved.
I am sure the variations on a shared understanding of the limits between family and close associates, and those that should be adhered to in public or workplaces, are broadly understood and applied by most. But as soon as anyone suggests there is a model language that meets all circumstances I am bound to say phooey. As many have said, react to anyone who offends, and if they continue to offend, pursue it, although in my experience few do. And if you are seeking to avoid giving offence seek out the preferences of those you are interacting with rather than lump them in to some common group.
And this is where I have a problem with what was reported about the attempts by QF to propose that there is a common language that avoids offence. You might reduce offence to some and increase it to others, rather than learn to adapt your language to your audience.