I'm not going to lie, I can't believe how many people are bringing this up. Not being able to hear Kilgrave isn't a good idea, not by a long shot. Being unable to hear him could be even more dangerous than being able to hear him in the first place. There are myriad things he could say and if you can't hear him, there's a good chance a lot of bad shit's going to happen. The reason Trish wore them was because Jessica was watching her back and Jessica didn't want anything to happen to Trish since she was using her, essentially, as bait.