I haven't played with nim for a few months, but only parameters with var will get mutated. I suspect you want to use someone else's cursed function and don't want to poison your blessed code
In bigger projectd and groups people need structure. If you're goal is provide success and structure for the people involved you can't let other people's lack of structure hurt everyone else. I think the "Kind of a Dick" is more of a cultural shock issue. You can be pleasant, but also blunt and honest about what needs to be done.