Even if they're not plants, there are tons of other issues

With the ongoing COVID pandemic many people deny, you can assume the crowd will be mostly science denialists, so the organizers definitely don't even need to do anything special to ensure a crowd of easily manipulated people

If people who actually disagree are allowed to talk, the idea must just be to psychologically bully them with how outnumbered they are in that location and reinforce the echo chamber bully psychology of all the people who came to feel the feeling of outnumbering someone