Just because it's been happening for a while doesn't make it right.
Why was Rafah a red line until all of a sudden it wasn't? Because he knows it's morally wrong and will lead to a lot of death but is too much of a coward to stand up for what he believes.
Honestly as someone who isn't American, this is more important to me than economic policy or whatever. I want Biden to win, Trump winning would be awful for everyone, basically worldwide. But most of all I want the kids to stop dying. I really don't think this is so unreasonable.
Trump won't be convinced. Biden might be. And this "less important" issue could still cost him swing states. I think maybe not supporting a genocide could be a vote winner.