Neither agreeing nor disagreeing with your general point about legitimacy, but there are a few big differences between monopoly money and bitcoin. I could fairly easily and cheaply buy a decent printer and print my own fake monopoly money that you wouldn't be able to tell apart from the real thing. Also, even genuine monopoly money could be easily printed in vast quantities by the makers if it ever actually became valuable enough to give them a reason to do so. You can't do the same with bitcoin. There is a known, genuine supply of bitcoin, a known schedule for creation of more, and forgery is impossible (at least not currently discovered to be possible).
