Do you think what a person says may be true or false based on their character?
Like if a mathematician is an objectively bad person, poisoned her own dog and voted for an evil president candidate, and if she makes a really cool discovery that can be objectively proven, will the discovery be less valuable? Should it be taught in school? Were Newton and Pythagoras nice people?
What if a moral teacher comes on a stage and starts to preach some leadership mumbojumbo, and then everyone discovers he molested a child? Would people continue to listen to him? Even if his words are universally true?
Now take the opposite situations.
Physicist who’s the most honest and nicest person you’ll ever know publishes a paper with a provable mistake — should their paper be disputed less strictly? What if it was a student — should they get a good grade if they worked really hard and visited every lecture?
Another moral leader, a person of a great character, gives a pure crap advice with all their best intentions — should we listen? Surely they are a very nice person and this should have worked for them.
Question the work first. If it can’t be proven, question the messenger.