It is common in both C++ and Java for a class to implement several interfaces. So, one can accomplish the same kind of genericity in C++ and Java as one can in Go. Both languages still eventually saw enough of a need for a kind of generics to develop one.

There is a difference in Go, and that is you don't need to explicitly implement the interface. That is, you don't need to declare that you do. But I am unconvinced that is so different from implementing interfaces in C++ and Java that C++ and Java programmers "need time and an open mind" to understand Go idioms.

Don't get me wrong: I think Go is a neat language and culture. I like many aspects of it. And I know the stance the designers of Go have on generics: they would like to do them, but they can't think of a design that they like. And they don't consider it that important, so they've bunted on it. They may do them in the future. But I find it strange when people who are not the designers of the language argue against having them, in any form.