I don't disagree. It's just more tedious in static languages.

Let's say we're doing a user registration. In most dynamic languages the JSON body will get parsed into a map. Excuse the fat controller and pseudo-language, but it'll end up looking something like:

    func create(conn, params) do
      if not Validator.is_email?(params["email"]) do
        return error(conn, "email is not valid")
      end

      if not Validator.min_length?(params["password"], 10) do
        return error(conn, "password must be 10 or more characters")
      end
     
      create_user(params)
      true
    end

In Go, if you want this nice and typed, you'd add a RegistrationInput struct with the field mapping tags:

    type RegistrationInput struct {
       Email string `json:"email"`
       Password string `json:"password"`
    }

Map the user's input to the structure, handling the error:

    var input RegistrationInput
    if err := json.Unmarshal(req.body, &input); err != nil {
      ...
    }

And then write the exact same validation checks.

What safety does Go's version buy you?