Without a harness, all an LLM can do is output text tokens. Nothing else. It's the harness that allows it to read a file, write a file, run commands, start subagents. But even a simple chat application would need a harness, because something has to take the input from the user, mark it up that it's a user message, then parse the LLM's generated tokens and display the message content, or diplay a referenced image inline, or whatnot. All of this is independent of any kind of safety or filtering of naughtiness.

Harnesses exist to give models tools to do work beyond generating text. People install Claude Code and Codex to have models work inside their repositories and run the code or tests themselves instead of the user having to copypaste code between their IDE and a chat interface. The fact that there's some security built into the harnesses is just a practical consideration, not its primary function.

The main role of the harness is not any kind of moderation or alignment, but simply making a text generation engine do anything other than output a long stream of text.

It's like saying that the role of a car's wheel is to hold wheel clamps. Yes, you can put wheel clamps (or snow chains etc) on a wheel, but the wheel's overwhelming role is to rotate and propel the car forward, and there is no driving without having wheels, you just have an engine with parts rotating inside. Bad analogy I know but, a harness is not a safety feature. Imagine that you're trying to explain cars to someone who has never seen one and you never say that the wheel's purpose is to rotate and move the car from A to B, you just say that it's something to put chains on when it snows.

I guess the name sounds like some kind of straightjacket etc. But think of it more as the harness you put on a workhorse or ox. It's the thing that connects it to the workload in the first place. They are not the blinders of the horse.