Please. Captcha by default. Email domain filters. Auto-block federation from servers that don't respect. By default. Urgent.
And yes, to refute some comments, this publication is being upvoted by bots. A single computer was needed, not "thousands of dollars" spent.
Regarding your edit, it can't be that easy since spammers could just generate thousands of AI-written responses to questionnaires
Right, an instance owner has to endorse another on an ongoing basis though. So for example, if an instance owner named Bob initially trusts a spammer based on a questionnaire, and then that guy immediately generates 100 bot accounts to start spamming with, then Bob can revoke the trust and the spammers instances get defederated.
You also need to own a domain to run a Lemmy instance. The cheapest of which are only a few dollars a year, which isn't much but it does put at least some floor on peoples ability to generate instances that'll just get banned.