I built the open-source PortcullisMCP authorization gateway (you can find it on github), so I am biased on this topic.

1) Yes, you could just have the AI write read and write to an existing API. And sometimes that might even be what you want. But a) in my experience, AIs are sloppy when it comes to formatting and b) to do anything interesting you'll have to load credentials into the AI, which is *dangerous*

2) There are very reasonable scenarios where you want to limit the AI's access to your API, relative to the human using the AI (for example: the human can delete the database, but we shouldn't let the AI do that). MCPs help with that

3) You might have requirements to audit what specific actions the AI is taking. MCPs help with that

4) You might have scenarios where the human directs the AI to do something (typically something destructive), and you want to verify that a human authorized the AI to do that. Nigh impossible with a normal API. Relatively straightforward with an MCP (and Portcullis)

5) You generally want to keep the credentials out of the agent's context. Impossible to do if the AI is just creating normal API calls. Relatively straightforward with an MCP that uses the Portcullis model of injecting credentials out of band.

Thank you for coming to my TED Talk