Of course MacOS asks you what you want to do when you copy over a folder and has done so forever. The keyboard shortcut to show hidden files has been mentioned already (it's even a logical one for once in Apple-Land) and the terminal command is straightforward and logical as well. Should they include a perma-toggle in the UI as well? I, personally, think yes but I also think it's pretty consistent with a certain approach to UI design to not include said button.