This is a very good point. When people ask me whether the Canadian Forces should be in Afghanistan, my response is “Do you think Canadian humanitarian workers should be in Afghanistan?” People usually say “Yes, of course,” and then I point out the relationship between security and humanitarian operations.
As I tried to point out, I don't see any natural, logical connection between how much money you provide for humanitarian operations and, necessarily, how much you provide for military operations. Each has its own demand and its own dynamic. As the opportunities and circumstances change, you change the application of resources.
How much is enough for defence spending? Nobody knows. How much is enough for humanitarian operations? Nobody knows, but the government of Afghanistan has an opinion on that and needs to be consulted too.