Intel's "redundant prefix issue"

Absolutely.

Common Criteria (CC) certification requires keeping the design confidential for example. Why? Because it forces an attacker into reverse engineering the particular device design, which is not impossible but definitely costly. And this will deter many attackers, all those who cannot justify the effort. In most cases security is not a binary proposition, it's an economic equation between cost of attack and cost of defense. And then obscurity makes perfect sense as a way to increase the cost of attack.

Everybody agrees "security by obscurity" is bad for algorithm and protocols. These are long lived, and we want the more review possibly to ensure strength and lasting protection.

But when it comes to a specific implementation, some amount of obscurity can be good, and can even be a requirement (see the CC spec)

For CC, I don't remember at which level it kicks in but for EAL4+ and above design secrecy is a requirement for sure, with requirements on how to control access and enforce this too. So you want to do an EAL4+ system? You must show your offices are properly secured for example, and that there are protection against tampering the design over the whole chain, from design to manufacturing to production. And most of this must be confidential, with proper access control.

So yes, I wish people would stop pushing "security through obscurity = bad" as if it were insightful. First, when it applies (algos & protocols) it is no longer insightful, everybody knows. And then there are plenty legitimate cases where it does NOT apply.

Always sane - Maybe. Always good - No.
By hiding how the system works, you forgo reviews that might find and/or fix issues. Whether or not that trade off is good is going to depend on the situation.
The other issue is that there can be multiple parties involved, whose threat models aren't aligned. While a sellar of a product might not want their competitors to be able to reproduce their product, buyers aren't going to care about that, but might have limited trust in the sellar and may want to be able to verify that the sellar isn't compromising their security. The sellar might also want to retain some control over the product after sale, while buyers will generally want full control of what they buy.
Sellars also care about making sales, so if buyers aren't buying their product because of obfusication, they need to balance that against how they benefit from obfusication.

Maybe... Just maybe you should consider not replying like this?

I deleted a lot of things I wrote before I pressed the "preview comment" button, but...