Those are opinions, not facts. Opinions are not facts. That's just what you think and feel, relevant only to you. Your opinion doesn't shoot someone else's opinion down, if they differ, that just means you disagree. If you disagree with someone, you come off douchey af if you try and tell them they're wrong, because you have a different opinion. You are better off (as in you come across less douchey) if you just ask people about their opinions, if they differ to yours, because, that expands your ability to understand more about the world. If you stay in your own little echo chamber, and never step outside your comfort zone, your mind stays small.

But to answer your other question, I would not say "that sounds likely false" to someone, that instantly puts you on the defensive and I actually want to know, if someone has different information than me, or has formed a different opinion, I want to know why. If I know they're definitely wrong, I ask questions that lead them to the conclusion, without having to say, you've been duped by propaganda, because if they aren't capable of coming to that conclusion on their own, they won't take it from me in another way, anyway. People don't respond well to being told, straight up, they're wrong, that's not a way to discuss, and it doesn't work to help people change their minds.