The short answer is: If you tell us that an e-mail from you is not to be trusted, we will honor that request. But if our system falsely catches an e-mail from you, say because of a bad SPF record, we will whitelist that sender.
We have a custom system I built and haven't yet had time to polish for a open source project (and it needs it before it could be publicly released). It has an awesome feature though...
Messages are rejected at the SMTP level, for things like SPF, greylisting, and SpamAssassin. The bounce message has a URL that the sender can visit to release the message. I was anticipating this might get abused and have to have a captcha on it, but so far it has not. Actually, it's worse than that, 99+% of people who get this message don't read any further than the subject, which is generated by their mail server, so they usually contact us some other way saying "Your mail server is broken".
BUT, the killer feature is that our users can go to a website and see the messages sent to them, and "release" them. So if you are looking for an important message no problem! You go to that page, type Control-F and the sender name or subject you are expecting, and click a button, and you have the message. It's kind of like a quarantine, but it's controlled by the sender AND the recipient.
Now, as far as what we do about senders that have broken SPF... We add them to a whitelist and tell them "You've been whitelisted, but your domain is publishing a notification that says this e-mail is invalid, you probably want your mail server admin to fix this because other places are honoring this as well."
No big deal, not ideological stands, we just deal with it and report it on.
Because that's the crucial thing: Your domain is telling me that this e-mail is not to be trusted. The CEO of our company understands that yelling "You can never have a false positive" means that they are going to have to deal with an inbox full of sewage -- they understand what false negatives are.