A short instructional YouTube talk by TJ Walker about how to disagree respectfully. Walker advises first summarizing the other person’s position (using their words to show you listened), then offering your own view stated plainly and value-neutrally so you appear respectful rather than rude.
Chapters
How do we express ourselves, our thoughts and our opinions, especially when we don't agree with someone without being rude? There are times when you have to communicate with someone and they're asking for your opinion, your analysis, and you clearly disagree with them. And yet you don't want to be confrontational. You don't want to be rude. The best way to do that is to start off by summarizing their thoughts. You don't have to agree with them, but you can let them know, I listen to you and I understand that your belief is and then restate their opinion. When you look at them and you use some of their words and you accurately summarize their position, they will feel listened to, they will feel respected. Then you can offer your opinion. You don't have to say, but I think you're a moron or I think you're completely wrong or your idea is stupid. Just state your opinion in a straightforward way, in a way that is as value neutral as possible, and they can conclude that you don't agree. But you will not come across as rude, you'll come across as respectful because you showed them you listened to them.