Unless you live in a swing state, just tell them that the presidential election is a sham election with a decided outcome already and given that it already has a decided outcome, lesser-evilism is inapplicable. Lesser-evilism, pragmatism, utilitarianism, consequentialism, and all the other -isms they like to throw around are completely inapplicable since all those -isms require a causal link between your action and the resultant outcome. But if there is no causal link, then whatever action they take is basically what they feel the action would be most compatible in a moral and just world. If they vote for Biden, they're saying "in my moral and just world, genocide of brown Ay-rabs is good aktually." A vote for Biden is functionally the same as turning in a homework assignment titled "why Biden is cool despite condemning millions of Palestinians to death." They could turn in any writing assignment like "why socialism is good" (this is the PSL vote) or "why sports showboating needs to come back and why people who hate showboating are loser nerds" (this is the Afroman vote), so the fact they've turned in a "genocide is good as long as Biden does it" essay means they absolutely deserve to get shit on.