Tell me about public blockchain apps that do not involve objective money or objective identity, which require strict global consensus, why they should be built on public blockchains, and why haven't they been built yet? I'll consider writing a post, when I get back to it, to explain why it does or doesn't make sense

I have read most replies, and I'm sorry for not replying to them individually. Generally, for most cases cited, I'm missing arguments for why strict global consensus is required - a lot of it can be achieved better with local consensus or just peer-to-peer, or hybrid apps with one or two elements on public chains.

To this point, I wonder if open-source security is one that requires local consensus on the state of your dependencies. If some dependency becomes malicious, all upstream packages should know that something changed.

As always, it depends. Each use case has its own requirements.

A one-size-fits-all approach is rarely a good answer.

Even for centralized services sometimes folks want to cram everything into a relational DB when a simple key-value store would be a much better fit.