[spoonjim]

The "Forwarded" note helps identify misinformation. If there's a message that says "2 Muslims came to my house yesterday, stole my baby, and ate her" and it comes from your friend you might actually believe it. If it says "Forwarded" you have a better signal that it's fake.

[bgdam]

The same 'Forwarded' tag can be easily attached to a message that is copy-pasted verbatim (atleast from another whatsapp message). Anecdotal evidence suggests that 'Forwarding' is just way too easy as compared to copy pasting an entire message to each person you want to send to. So forcing people to do this would indeed reduce the amount of misinformation being spread via unvetted forwards (at the cost of 'valid' forward messages - which I think are too few to matter).