Why are actresses called actors now?

In my last blog I wrote about a film actor and actress, and found myself irritated yet again by the, to me, utterly ridiculous convention which appeared some years back out of nowhere, and I hope may at some time in the future disappear as quickly again, that of calling actresses actors. Is this political correctness gone mad? We still distinguish a husband from a wife, a girl from a boy, a widow from a widower, a prince from a princess, so why not an actor from an actress? Of course some professions only have one word to describe both male and female practitioners, such as a barrister or a doctor, perhaps because women were only admitted later to these professions, whilst actresses belong to a long tradition. And nobody appears to have thought of calling a female barrister a barristress or a female doctor a doctress, although this is what other languages do. But why replace a perfectly good word which has been used for centuries? And in an obscure way, I find its removal to be demeaning rather than respectful to women, as though we all need to make an effort to remember gender equality.

Interestingly, the convention has not yet crept into everyday speech, where people still talk about the actress Judi Dench, but in the written press and on radio or television it has been banished to the archives, the latter obviously by BBC edict. And yet I was amused the other day to hear a journalist stumbling over himself, the word “actress” coming out unbidden, before being quickly corrected to “actor”.

Can anybody tell me when and why the change from actress to actor took place?

Postscript to this, added today, 7 July:  I have read the following in the Independent of 5 July:  "...two of Hollywood's best acresses, Helena Bonham Carter and Gillian Anderson,...."!