The problem with Emmeline Pankhurst is that her leadership of the suffragette movement seems to have been romanticised by the popular imagination. From what I have gleaned from various tweets and comments, there are many who are under the impression that Emmeline Pankhurst won the women's right to vote in Britain. Which is simply not true. For one thing, there has been no mention of the non-violent suffragist movement, led by Millicent Fawcett, which actually had a lot more support. For another, women's suffrage was not granted as a direct result of the actions of the two organisations (in fact, the suffragettes arguably harmed their own cause with their endorsement of hunger strikes and vandalism); effectively, it was in WW1 that women proved that they were capable of doing men's work, and therefore equal to men.
But even though I disagree with Pankhurst's suitability to be on a banknote, it's actually kind of irrelevant. Churchill is another figure whose virtues have been exaggerated almost to the point of apotheosis, resulting in lots of his cheesy quotes being plastered all over Pinterest. In reality, he did have flaws and made decisions that I don't necessarily agree with. However, at this moment in time he has a unique presence in the British consciousness as a kind of national icon. Personally, I think I'd find it a bit weird if he never made it onto a banknote.
I don't think that the Bank of England are taking a step backwards on women's rights. I don't think a woman should be chosen to go on a banknote just to fulfil some kind of equality quota. That doesn't mean to say that I don't think there are plenty of women that should be there: Mary Seacole is one example among many that should definitely be considered. What I mean is, we've read the situation wrong. This isn't a woman being replaced by a man; this is a human being replaced by another human. It would be tedious to argue that Churchill shouldn't be on a banknote, so why should we change it to a woman, purely because she is a woman? If anything, it's sexist, and if we truly believe that men and women are equal, it shouldn't matter. Respect should be gained for your person, not your gender.