This is the mod's responsibility , all what we are somehow morally obligated to do is report these incidents , i understand that your intention is to reduce low quality content, but sadly your tag does not accomplish it, the user will still be able to post whatever they want in the ANN section and now even in Meta because of the tag he got.

you spent the time to read his posts and seems like you were fairly confident that he is a spammer, i think if you reported a few posts of his or if you happened to find plagiarized content and reported those to the mods, he would have been already banned .

having said that, i still stand to my opinion that while this user might deserve to be banned, he does not deserve a negative at all, simply because he is not a scammer but rather a spammer.