There are a few different things I'd like to mention:
I don't think, that there is such a thing as a massively defederated instance exists right now. The most blocked instance is blocked by about 11% of the instances, followed by two instances at 6%
Even if the die hard scene users would know their instances, not every random troll or spammer would.
This doesn't address the possible legal issues of publicly announcing where someone could find illegal content
And lastly: If you're new to the fediverse you maybe shouldn't run your own instance in first place. Helping reckless people pull reckless stunts is a bad reason to promote a feature.