"Report spam" is quicker and easier than "unsubscribe".
Gmail added a popup asking the user if they want to unsubscribe when flagging a newsletter with the appropriate unsubscribe headers, so it must be common enough to warrant Gmail developer attention.
> Gmail added a popup asking the user if they want to unsubscribe when flagging a newsletter with the appropriate unsubscribe headers
Unfortunately close to 100% of the spam I'm flagging causes this popup now :-/
I'm getting a dozen spam a day now on my Gmail account ... I think they're losing the battle.