I don't find your example very convincing. Any database storing personal data needs to be properly secured, and if that gym also has ID credit card or other more sensitive data, that data might better be destroyed than stolen.
If it's a publicly accessible wiki with no sensitive data whatsoever, and that's meant to be publicly accessible, then there's a reasonable excuse for the poor security and it's not helping anyone to destroy it.
The point is that, if my credit card info is staying in a web-exposed, insecure DB, it is safer for me that it be destroyed than left alone.
I have no idea of that is the intention of the attackers, or if they are maybe even stealing the info before deleting it. But assuming they were good Samaritans and just deleting it, that is the best outcome for me as a user, better than if it stayed up for another day.
If it's a publicly accessible wiki with no sensitive data whatsoever, and that's meant to be publicly accessible, then there's a reasonable excuse for the poor security and it's not helping anyone to destroy it.