It seems that all of a sudden this song became controversial, but I can't see the problem with the 'Beat her, mistreat her' lyrics if you put them in their correct context. The storytelling just changes perspective, and there clearly are two people telling the tale.
The song begins with an elementary, but hammering guitar ostinato over which Narrator 1—a man who knows Charlotte—invites people to 'the place where we all go', Charlotte's place down in London's East End: the number 22 of Acacia Avenue. Side note: there's a bit of uncertainty here on whether or not Charlotte kept the same prices she used to charge in 1980: in 'Charlotte the Harlot' she 'charge 'em a fiver, it's only for starters, and ten the main course', and now (1982) 'fifteen quid is all she asks for'. 'Ten [for] the main course' probably means that in 1980 it used to be £5 for starters + £10 for a complete intercourse, but there's a small possibility that it means that you could have had preliminaries for £5, and a complete intercourse if you doubled down, making it £10 in total. Such ambiguity should discourage one from using Iron Maiden's lyrics as tourists' guide when doing their pilgrimage to the East End.
Anyway. Charlotte is a prostitute and the lyrics make it very clear that she 'is' open to rough/unconventional practices ('Everybody got their vice')—or more likely, her pimp allows the clients to do 'anything that they please'. He's clearly a barker and the way he introduces us to Charlotte dehumanises the lady, almost as if she's a toy: Narr1's words focus on how much will she cost to the client (but don't worry—she's cheap), on her place being popular (so what are you waiting for? We're all there already); there's always a lot of people there, but if the queue's long, just tell her you know him and she'll be happy to give you a special treatment.
Narr1 is almost certainly Charlotte's pimp, advertising her to potential new clients. This is emphasised by his vocals turning almost anthemic when he first mentions Charlotte ('Meet a lady that I know!') and the special discount you can get ('You might even get it free!'). Notice also that as soon as his hook got our attention, he starts to advertise her, just like a salesperson: are you looking for a good time? What do you say? A price to pay? Well of course but it'll be cheap!—And: are you going to the East End? Don't for a moment hesitate! Honest to God, it'll be wonderful! And you can't imagine what she can teach you...
Then the music shifts to more melodic/hard rock riffing, which coincides with the more empathetic Narrator 2. For simplicity's sake, this guy can be identified with the narrator of 'Charlotte the Harlot', who met the girl and fell in love with her. In the previous song already he was asking Charlotte to question her life choices: 'Sticking with every man that you find, don't you know what they're after?' 'You're taking so many men to your room, don't you feel no remorse?'
This occupies two verse-chorus sections where we're given a perspective more similar to that of the first song, and especially of its slow interlude: Charlotte's place is no more just a brothel, 'it's warm inside' (most probably a double-entendre). She's sexy and provocative, people turn their heads when she walks down the street, she eats her men and spits them—but she's slowly spiralling down to madness, this dissolute life will eventually take the toll on her once beauty, why she does it? Does she like it? Or she just needs the money?
Then after the second chorus, the music suddenly becomes more aggressive, almost punk—the creepy Narrator 1 is back. It is him who's speaking here, 'everybody got their vices' he had said, now what's yours? You want to beat her? Mistreat her? Bite? Abuse? Make yourself at home, 'do what you please', who cares, she's just a cheap whore after all, that's why she's there and let's be honest she likes it. Charlotte is dehumanised again. She sticks her arse and legs in the air for fifteen quid, might as well treat her like a doll.
At this point Dave's bluesy, solo kicks in, and his melodies depict a tragic picture. Maybe Narr2 wasn't wrong. This life's definitely gonna kill her. The solo ends and the song builds up again and Narr2's riff comes back. The man tells Charlotte to leave that 'mad life' and come with him. She refuses at first ('You're running away, don't you know what you're doing? Can't you see it'll lead you to ruin?'), he insists.
Did he succeed? Maybe. The lyrics close with an open ending, but if we consider 'Hooks in You' the third chapter of the Charlotte saga, he could be the same man who'll eventually murder Charlotte out of jealousy.
So long story short. That verse is definitely uncommon in Iron Maiden's lyricism, and fine, it can be uncomfortable to many. But I wouldn't call it unfortunate. There's a reason why those words are there, and it's not necessarily misogyny of its own sake. The East End wasn't the best place in the world after all, those lyrics could even be considered brutally realistic.
