It's just how liberal centrists sheild themselves from self-reflection. They know there are people to their left, and engaging with their ideas might make them realize their policies and candidates cause harm, so they decide to dismiss them out of hand as aiding the right. This creates a safe narrative where they're always the good guy; people to their right are dangerous lunatics, people to their left are naive fools who are unintentionally helping the lunatics, and they're the only ones behaving responsibly. This allows them to condemn people calling for the end of a genocide without engaging with the fact that their candidate is enabling a genocide.