Sorry for the wall of text.
I honestly do not think that your judgment was accurate in this situation, and I think that you jumped the gun; the poster sounds genuinely clueless. However I’m fully aware that I don’t have full access to all the info necessary to conclude shite here.
Large bans don’t decrease your workload, they increase it.
Trolls and bad faith agents might wait for a short ban to expire, but they won’t wait for a large ban - they’ll evade it with an alt account and call it a day, and now you’re playing whack-a-mole with them. With a permaban at least you’re telling them to fuck off, even if they won’t listen.
For more sensible users, the large ban is unfair, and conveys “we still want you here… but we’re too lazy to deal with you thing right now, so shoo”. Other users are not blind, they will notice that the mods overreact to rule infractions and they will avoid reporting things, except for petty reasons. Now you’re bound to fine-comb threads manually to enforce the rules because nobody is reporting shite.
Either way, you’re doing more work than you would otherwise.
A better approach here would be to contain content prone to trigger rule-breaking comments. Megathreads work like a charm for that; they allow you to fine-comb a single thread instead of the whole community. It also helps to bring up the content diversity of the community.
Another thing. I do agree with you that automatically tying that chant to Antisemitism is itself Antisemitic; however you’re taking for granted that all users are on the same page when it comes to that, and both of us know that the media is spamming them with misinformation that conflates Israel with Jewish people. In those situations it’s better to issue an official statement, explaining what will be considered Antisemitism for the sake of rule enforcement. (It helps to inform other users too.)
Fun fact: strawberry was admitted to the psychiatric yard once pepper and cucumber joined the berry club.