This isn't about the benefit (or perceived benefit) to society, it's about the benefit (or perceived benefit) to the individual. That's really the ideological debate at the heart of this particular issue, as whilst strict gun control advocates believe their position would on balance be better for everyone, those who are for gun liberalisation believe their position is better for themselves.
It's individualism vs communalism at its basest, really.
You are absolutely correct, in my estimation. But what is a society but individuals? How can you say society is protected if the individuals who comprise that society are not? And how many individual lives are worth losing to protect "society"?
Let me phrase it this way: let's say that you're correct that more people would be saved with gun control that would be harmed. What would you then say to those that were harmed? "It's okay, because society is protected"? "Isn't it great that, despite the fact that you're hospitalized and may need years of therapy to recover, that other people who weren't even involved in this incident are safe"?