BBC4 Extra is one of my favourite radio stations, mostly because of the re-runs of comedy shows from the 1960s and 70s. Quite often, the continuity announcer will set up a programme by making reference to "humour of a different era", letting first-time listeners know they may hear words, phrases, jokes and slang they might find offensive.
One of the most popular variety programmes in the BBC's history was The Black and White Minstrel Show (it ran from 1958 to 1978 with regular audiences of over 20 million), featuring singers in blackface make-up.
As early as 1967, the Campaign Against Racial Discrimination presented the BBC with a petition accusing the programme of racism and asking for it to be removed. It was to be another decade before the programme disappeared from the schedules, yet the show continued live tours for a few years.
In the past week, following on from the Black Lives Matter protests, a number of celebrities, including Keith Lemon and Ant and Dec, have apologised for using blackface in their shows; while the hugely popular Little Britain has been removed from BBC iPlayer, Netflix and Britbox due to use of blackface (almost 25 years after The Black and White Minstrel Show was axed).
On Tuesday, HBO announced that Gone With The Wind would be pulled from its schedules for a while. It will return soon, but include "a discussion of its historical context and a denouncement of those very depictions. But it will be presented as it was originally created, because to do otherwise would be the same as claiming these prejudices never existed. If we are to create a more just, more equitable and inclusive future, we must first acknowledge and understand our history".
The past is a problem: always has been and always will be. Yet, as L P Hartley noted in the opening lines of The Go-Between: "The past is a foreign country; they do things differently there."
Having done things differently doesn't mean that what was done was politically, or morally, justified, but it does raise problems when we look back and try to judge the values and behaviour of our predecessors.
As Hugh Laurie tweeted yesterday: "For every hour we spend agonising over societal crimes of the past, we should probably allow a minute or two to wonder what we're doing now that will be similarly condemned a hundred years hence." He's right: never look at the past when you're sitting on a high horse.
But in the rush to condemn the past, we sometimes forget there were always movements and individuals who challenged the "norms" of their day and risked their lives to force governments to rethink and reform.
I've seen it in my lifetime: civil rights campaigns across the world and in Northern Ireland; the legalisation of homosexuality and same-sex marriage in many countries; relentless campaigns against discrimination on grounds of race, belief and lifestyle. And in many of those campaigns, it was clear that lessons had been learned from the past. As it happens, I have no particular concerns about the removal of some statues. I can't think of a single argument to justify the glorification of anyone who made their fortune from the slave trade, for instance - no matter how generous their philanthropy was to a university.
But are we reaching the point at which the beliefs and past actions of every philanthropist must now be put through the wringer to ensure that some group or other isn't offended here and now? Or that some group won't be offended in 50, 100, or 150 years' time?
There is a danger in removing the past simply because it has been "reassessed" (a wonderfully Orwellian word, don't you think?) and deemed unacceptable to a modern audience.
Churchill remains a hero for millions in the UK, yet millions of others detest him and want to pull down his statues.
Who makes the call on something like a statue? Who decides what is acceptable a generation, or couple of generations, later? Who signs off on what parts of our past we want hidden and forgotten?
It isn't just about statues. It's getting to the point at which anything which is now deemed offensive to a modern audience may just be removed or "reassessed". Films, books, TV programmes, comedy shows, individuals, politicians et al will probably go on lists.
And I don't just mean race issues. Almost anything will be considered fair game from the perspective of hindsight.
But in sweeping away key elements of our history, you also sweep away the background story. Crucially, you also sweep away the history of those who fought against previous injustices; for you can't just keep one side of a story and hope it makes sense to a new audience.
Great wickedness was inflicted upon millions upon millions in the past. To stop it happening again, we need to be aware of the wicked and their methods.
Removing the past because it doesn't suit some narratives is never good. How do you learn from the past if we simply wipe it away? Do we remove great art, literature, or films, because someone has been offended?
And with society increasingly diverse and searching to protect that range of diversities, a book could be acceptable to one set of self-identities, yet offensive to others.
Does it go? Who makes the decision? Do we get to the stage at which it will become impossible to maintain freedom of speech, because the restrictions governing what we write, say and do will be too cumbersome?
How long will it be before the argument is made for removing some people from history, like Nigel Farage, Enoch Powell and Tommy Robinson, for instance?
Someone for whom I have enormous respect told me that social and mainstream media should begin to "de-platform" those he described as "extreme" and that publishers of newspapers, magazines and books should not even mention them.
His reasoning: succeeding generations should not have access to "the appalling views of people like that". Reactions I have heard over the past fortnight suggest he is not alone in his views.
But we cannot control and should not try to rewrite the past (although recognising previous wrongs and ensuring they are not repeated is vital).
We cannot pick and choose which parts we deem acceptable. We cannot say what we would have done, or thought, had we been alive a century or so ago.
Apologies from celebrities for "unintentional" offence won't make a damn bit of difference to anyone suffering discrimination right now; and nor will a tidal wave of virtue-signalling from people and politicians who feel a need to be seen to do something.
Sadly, instead of focusing on the racism which still seems endemic across parts of America and wondering how we can collectively address it, the ongoing protests have become about a number of other issues altogether.
That often happens when the present and past collide; and, too often, it leaves the oppressed no better off. The past is always difficult. There are no easy answers.