>There's nothing particularly special about it other than it being an explicit choice

Yes, this is what I meant. Go is explicitly designed according to the philosophy that it is beneficial overall for every type to have a default zero value. You may disagree with this, but if you find you are constantly fighting zero initialization, you should probably just use a different programming language.

>Valid doesn't mean correct.

I understand that. However, in most cases, you can arrange for zero to be a valid value. It may require a little creativity, but it's rare for it to be impossible in my experience.

As to packages, I still don't see the issue. The related types can be in subpackages of a parent package. And as you say, it's simple to create packages.

>So at the end of the day, people don't do it and instead elect to be "more careful", which isn't a good method of preventing bugs.

I don't think this choice has anything to do with the overhead of packages. Most people just don't like the style of 'bondage and discipline' coding where the type system is maximally exploited to enforce every possible invariant. Again, this is just fundamental to Go. It was designed by people who have explicitly said that they don't see value in using the type system this way.

By the way, I am no stranger to the possibilities in this space, having been paid to write Haskell code for a while. I've even done absurd things with the type system like this: https://adrummond.net/posts/cooper However, I tend to think the Go folks are right on this. It's good to have a basic type system, but there are rapidly diminishing returns on the fancier stuff.