I really dislike languages which decide to bless some special data-structures, but then won't let me add my own generic data structures.
Of course, I really love data structures, so I can understand other people who just want to get on with things, and are happy to slightly abuse some built-in data structures to get most of the way there.
Go doesn't stop you from building datastructures, actually is really nice for building datastructures.
It simply doesn't provide a simple way to build some kinds of generic datastructures, but when the ones provided by the language are not enough it usually means your problem is specialized enough that a custom datastructure is best anyway, and Go makes that pleasant and easy.
And then there are interfaces, which are a kind of "generics" of their own.
I don't like the special treatment for builtin data structures either. But if the alternatives are ending up in a mental institution (C++ templates) or in a Potemkin village (Java), I'd rather live with this inconsistency for a while.
Maybe (hopefully!) these are not the only alternatives.
Of course, I really love data structures, so I can understand other people who just want to get on with things, and are happy to slightly abuse some built-in data structures to get most of the way there.