That's silly, in my opinion. I'm not going to argue about any brilliant plot machinations conceived by Stieg Larrsson, because while the book may have a riveting mystery on a purely surface level, it's a terribly written piece of trash that is beach reading at best. What it does well is spend time building up character profiles, motivations and interactions. So I'm not going to argue too much against "raped woman has justification for revenge" and how that effects an audience.
However, to claim the intent of the film is that it wants you to believe a woman MUST be raped twice in order to have her concerned about catching serial killers is an intent I believe you're placing on it. What the rapes do is create a partial character profile and provide partial motivation. Lisbeth has no reason to want to help Mikael, her victimization gives her reason to.
Are there others ways to do this? Yes. Would a better writer have created more ways? Yes. Are there other motivations within the film? Yes. Are they shown as being more important? Not really. But Larrsson also wanted to portray the brutality that is often seen in state wardship and how the (arguably) mentally ill or those in vulnerable positions (especially women) are often treated by those in power, and by the patriarchy, and how that can often be predatory. So he wanted to work this plot element into the book.
Again, is it a good story? No. The characterizations are interesting to me. But the book is not well written at all. I think Zaillian, Fincher et al made an admirable attempt at an adaption, though. I do not think anyone involved is TELLING you a woman MUST be raped to CARE about murderers, though.
