Instances, of course, have some bot-mitigation tools which they can use to prevent signups, etc.

However, what’s stopping bots from pretending to be their own brand new instance, and publishing their votes/spam to other instances?

Couldn’t I just spin up a python script to barrage this post, for example, with upvotes?

EDIT: Thanks to @Sibbo@sopuli.xyz ‘s answer, I am convinced that federation is NOT inherently susceptible, and effective mitigations can exist. Whether or not they’re implemented is a separate question, but I’m satisfied that it’s achievable. See my comment here: https://programming.dev/comment/313716