Former anti-spam guy here. Spam is hardly something everyone agrees on. There are big grey areas where people spam without thinking they're spamming, and yes they do get upset about it.
The primary moral and legal defence the big email providers have with respect to spam filters is that they're essentially democratic: they're powered by user reports. So if someone complains to Google that their mail goes into the spam folder, Google can just say "it's our users fault, figure out how to make them happy" and that's a good answer that puts them back in the driving seat. Also, users can whitelist mail if they disagree with the mail providers opinion. Spam is ultimately not a matter of politics then, it's a matter of aggregate user opinion on what sort of mail they want vs don't want.
This particular issue seems rather different. There are no user votes involved here and it's unclear why you'd want such a system anyway, given that people who disagree with a website can just not visit it. There is no way for visitors who disagree with Google's assessment to access the site anyway. And so on.
My understanding was sufficiently bad spam mail got dropped and never got into the spam folder to begin with.