There is one case where differentiating makes sense: Sometimes users sign up for newsletters, want the newsletters, would re-confirm if asked... and later chang

There is one case where differentiating makes sense: Sometimes users sign up for newsletters, want the newsletters, would re-confirm if asked... and later change their mind and no longer want those newsletters. Here, marking as spam is unreasonable. In most other cases (e.g. newsletters sent based on a tiny pre-checked checkbox or without asking for consent), the spam button is of course the right tool.