Convince who? Reasonable people that have any sense in their brain do not have to be convinced that this behavior is annoying and a waste of time. Those that do it, are not going to be persuaded, and many are doing it for selfish reasons or even to annoy maintainers.
The proper engagement (no engagement at all except maybe a small paragraph saying we aren't doing this go away) communicates what needs to be communicated, which is this won't be tolerated and we don't justify any part of your actions. Writing long screeds of deferential prose gives these actions legitimacy they don't deserve.
Either these spammers are unpersuadable or they will get the message that no one is going to waste their time engaging with them and their "efforts" as minimal as they are, are useless. This is different than explaining why.
You're showing them it's not legitimate even of deserving any amount of time to engage with them. Why would they be persuadable if they already feel it's legitimate? They'll just start debating you if you act like what they're doing deserves some sort of negotiation, back and forth, or friendly discourse.
