actual evidence
The reason why I think Harris is better is mostly that the people commiting the genocide prefer Republicans. You can also look at differences in their rhetoric.
But I disagree that you need reasonable evidence of a meaningful difference. If you have a binary chose in a situation like this, you ought to pick the one that you believe to be better, no matter how unsure you are.
If you got dragged in front of a war crimes tribunal for participating in a genocide, a hypothetical argument that someone else would have done even worse wouldn’t actually excuse you, same as it wouldn’t for any other crime.
This analogy does not work because someone participating in a genocide does not just have a binary option. If they refuse to act, the genocide will slow down. This is not true of an American voter. Refusing to engage in the binary chose only helps the worse of 2 evils.
Your argument basically sets up a justification for voting for any evil- kill LGBTQ people, kill Socialists, kill disabled people, etc- so long as you can argue that someone else would have been worse.
I disagree. The argument needs to be that voting for anyone else would have been worse.
If course, all of these arguments only apply to voters in one of the 12 battleground states. Other voters do not decide who is elected, so they ought to vote 3rd party to attempt to change the policies of one of the major parties.
Less than a month before election day, we have enough data to know that either Trump or Harris will win. Voting for someone is not an endorsement or showing support for them. A vote ought to be a strategic action, optimizing for outcomes you would like to see.
For me, this means voting for Jill Stein, because I live in Oregon. But if I lived in Michigan, I would vote for Harris with a clear conscious. If you live in a battle ground state, voting is too important to be used as an expression of values.