I’ve not worked with Go (although I did read The Go Programming Language), but use in a library is a different beast than use in an application. In Java-land (where I make my money these days), I would reject any pull request for application code that used reflection but at the same time, I happily use libraries that push reflection to its limits.

To take one common use case for reflection, Json marshalling/unmarshalling, if I were writing an application that needed to do this, and for some reason I could not use a library, I absolutely would not use reflection, but would write code that specifically targeted the classes that I was marshalling/unmarshalling. Conversely, if I’m writing a library, I don’t know what those classes are so I must use reflection to manage this. That’s the key difference here.

You aren't writing std lib.