You are in a bubble of like minded people, your anecdotal experience does not apply to all people.
> The only kinds of people that react positively to witnessing mockery are the types of people that political movements would do their best to avoid: people that take pleasure in witnessing the denigration of others.
That's well near half or so of the voting base; try and step outside your own limited experience, everyone isn't you. Trump supporters for example very much respond to mockery, they liked that Trump mocked the other republican candidates in the primary and were swayed to vote for him based on what appeared in their eyes to be a strong performance in the debates with his peers.
Frankly, you're giving people too much credit and failing to recognize that much of the population isn't very mature. Of course it's childish, that doesn't mean it doesn't work. You don't live in a country full of mature adults.