For me, this song doesn't tread the "romance of crime" path as some believe it does. The meaning is deeper than that. In this song, Morrissey demonstrates the very vastness of his understanding into human relationships and behaviour.
First, the title "Jack The Ripper" is a provocative one, but I think we do the song an injustice by taking it solely literally. Rather than being about the killer and white-chapel murders, I think Morrissey uses it as a metaphor for the predatory danger of the cat-and-mouse game between aggressive pursuer and attention seeking lover. "You look so tired/mouth slack and wide" and "you don't agree/but you don't refuse" articulate this side to the song, and the "I know you" is suggestive of the sexual politics involved in the chase. How it is all a game.
When I listen to the song, I'm always reminded of an incident I suffered a long time ago: a girl at a party got very very drunk and left in the middle of the night, and began wandering in a stupor around the streets, down alleyways etc. She had suffered the break up with her boyfriend earlier that night, and I think she felt depressed and upset, so left. I went out to bring her back with some friends, and I found her alone down a particular street, and when I asked to come back, she began making propositions, if you get my drift. I didn't do anything, obviously, except for the sensible thing of bringing her back, but it seems to summarise the subject of the song: Playing the victim puts one in not only a position of vunerability, but also power. The pursuer is therefore at the mercy of his/her baser desires and faced with a moral choice in such a confrontation. It's a very subversive idea and one that Morrissey expresses so well.
When he sings "Crash into my arms/I want you" therefore, he could be singing from the perspective of either character. This is why the metaphor of "Jack The Ripper" is so important, it's deliberately subversive. I love this song because it stuns me with it's understanding and sheer insight into irrational sexual politics, desire and nature of human behaviour. It's systematically sinister and romantic.
And it was a b-side!?
You're right of course. I think the best part is that the real meaning of the song is so subtle. I wonder if anyone's played it at their wedding? 
