So let's say there is someone in a public setting that is using a traditional microphone and speaker setup so that they can berate passerbys. What method would I need to approach with in order to prevent them from speaking through a microphone while I'm in the area?

Technically speaking, I know that wireless microphones are required in the US to operate at VHF or UHF ranges. However, I believe that VHF/UHF jamming, even short range, would be illegal per the FCC. I suppose I could receive the microphone's RF and then retransmit it, creating multipath interference, which would then make the speaker unable to talk which isn't technically jamming I don't suppose. But I don't want to test the law with that.

Could I set up a microphone, tune it to their channel, and then just allow that microphone to create its own interference?

What about about people with megaphones, or wired mics?