Turn on the TV. Try repeating what someone talking continuously says right after they say it. That's what happens; it jams you mentally. Granted simultaneous translators at the UN do it with a twist, so it's possible.

(AFAIK, this is why deaf people find it hard to speak.)

I guess public speakers could also have their speech pumped directly back into an earbud (like live music singers).

People who have been deaf from birth or youth find it hard to speak because they don't have the experience hearing others pronounce words which lets them develop proper pronunciation (similar to how non-native speakers have an accent).

People born with normal hearing who have lost their hearing due to age or noise exposure have no problem speaking.

In general, I am not sure that the claim that this is going to prevent people from talking very effectively. Maybe it will be uncomfortable, but with a little bit of training and earplugs would not be effective for too long.