And the only email I want blocked is a domain where every single user is malicious, not a domain run by a malicious entity which has normal people as users, who aren’t necessarily very tech literate.

You'll never get the tech iliterate people to switch to the rest of the Fediverse otherwise. Defederating Threads is about making it as bad as possible for its users - it's about hurting Meta and stemming its bad influence on the web.