I failed to take into account that letting spam through encourages spammers to simply send more spam. Thanks for explaining that as it illuminates a lot (admittedly, my ideas on how spam could be handled are likely naive and uninformed, which is why I ask a lot of questions and wonder openly about a lot of things - there are probably good reasons my ideas are impractical or just plain undoable but I can't envision what they are without looking a lot more into the topic).