We all gotta unsubscribe from this attitude where everybody thinks the way to serve the deluded is to humor them. To humor them, and maybe include subtle hints and jokes in your responses, for them to "note the conflicts" and "figure it out for themselves."
Honest and direct people depend on each other to tell truths. To offer resistance and to ask questions where truth told seems wrong. This is how grown-ups learn: exchange of views. Give YOURS. Hear THEIRS. It is not: tease theirs incessantly, in hopes a change comes over them to yours! Honest and direct people don't humor another where they know they are wrong. They offer their help, and their curiosity too. They point it out, and wait to hear what the response is. You have zero excuse for enabling in another what you yourself regard as falsehood. It's not educational - and this isn't school, sir.
No one has selected, hired, certified or sanctioned you in any way as fit to be another's teacher, out here. Or are you a professional educator? Your ability to teach in that context means nothing outside of it. Hiding and dodging and fake encouragement, hints and peekaboo, with no lesson plan in place - this is no part of any approved learning curriculum, certainly not outside your classroom. This isn't done with any legitimate goal for the other's growth, learning or development. It's done in cowardice, a vote of "no confidence" in one's truth (or one's grasp of it), or out of sheer disinterest in the other's well-being.
If someone comes to you with what you know is wrong, you have some good options.
Option one. A direct block to the delusion, based in where you can see it's wrong. First, take their delusion and state it clear, so we're on the same page. You don't have to call it a delusion. The fact you conceive it in such terms shows perfectly well you believe you "know it's wrong." It remains for you to demonstrate where. Second, once we both hold the same idea of the delusion, get agreement on some underlying reality. Use a reality which they too see - the observable reality, available to the senses for any to see. Get agreement first on that piece of reality you intend to use. Both see it? Both looking at the same thing - the same uncontroversial, universally-viewable flat-fact-in-the-world THING? Great! Third. If you are not full of shit, take that underlying reality and use it show and tell - not "your truth!" Your truth is as worthless as you think theirs is! Fuck your truth. Use everybody's fucking truth. Show the conflict you can see, where their idea can't be made to fit.
Option two, very similar. If you're not one to offer a direct block, still you can direct question to it. Without agreeing to it, without encouraging their delusion. Leave out the direct demonstration of conflict entirely. Ask instead about the parts where you see conflict. Ask with reference to reality-as-demonstrably-shared between you - you still want to use the agreement-on-reality step. From there, ask direct questions. Ask with a sincere desire to know. Don't ask "how do you explain THIS??" Ask questions that explore the ways they see it fits in their eyes, in their mind. That tell how they came to that grasp of things. Use what they say to lead into the next thing that confuses you, about their view. You will find out how they continue to hold it. This is understanding that's worth the effort. And what believer doesn't love to lay out their belief, to the serious and curious?
You might learn something, you know. So ask honest questions only. An honest question is one that admits of more than one possible answer. An honest question is open to the possibility they may have a true answer that you don't know, yet.
If the other person begins to experience frustration, and inability to answer, you can always stop. You were not hinting and encouraging them in their delusion. You were asking honest, direct questions - and you were sincerely curious, as to how it all fits together for them. You were willing to hear their answer, and are open-minded enough to believe you might even understand it - that it might make sense to you. Even if you still see an irreconcilable conflict, your understanding of them will show you why they may not. Worth knowing. Worth sharing. It will apply to many others whom you've been previously unable to understand - although, don't make the mistake of believing everyone comes to the same "truth" the same way, and holds it for the same reasons! Even for truth without the scare quotes, this is not the case.
If the questions themselves become troublesome, if the other becomes frustrated, you can let it go right there if you like. Maybe return to less troublesome areas, where you'd been agreeing and sharing views easily. Let that be your day's work. Leave the trouble and the questions with the other. Because you spoke and shared and questioned respectfully, the other will have a way into them, and may be able to work through their troubles. They may even come back to you later for more!
Neither you nor they will ever learn a damn thing by you humoring their delusion: arrogantly, ignorantly and maliciously pretending to them as if you think it might be valid. Cowardly. Never put out there what you truly believe and know. Never lay out your best courageous truth, where the other can see it. Just drop humorous little cryptic hints for them to figure out for themselves where you think they're wrong. No sincere openness to the possibility they're right! You're not afraid to give your truth because you honestly respect theirs, and believe it could be valid. Naw, you know better than that. "This poor fool is deluded! A known delusion has got them by the tail. They must figure it out for themselves! It's the only way."
People go through life in a world full of cowards like you, all of them bent on withholding their precious truth from each other, on humoring the other's delusion in a pretense of honoring its possible validity. Why? If you can't offer an honest block, or a direct question, why not just shut up and change the subject? If pressed, simply admit and profess what is true:
You have no confidence in your knowledge in this area.
No interest in improving yours or their grasp of truth.
Your grasp on truth is too weak to oppose to delusion. Your hold on truth is nothing you feel confident to test.
Your desire or ability to learn is too weak to even question others sincerely, as to how their view fits into reality we both can see.
Your truth is too weak to share.
I wouldn't worry. Almost everyone around you is in the same boat. They probably won't confront you, or oppose your weak and weakly-held truth. Their truth is as weak, and as weakly-held. They too secretly fear demonstration, fear direct comparison of their truth with reality. They know they cannot show where their truth is, or where conflict exists, show how a truth fits or fails to fit into reality. It's not because they're stupid or anything, it's just how we're reared. We're raised not to care about someone else's delusion.
It's a dodge to cover how much we suck at sharing, questioning, testing, and rejecting claimed truth. If you care about someone and they're blithe in the grip of something you know and can show is wrong, and you won't do it, go back again to the start of this sentence, and start over with no. You don't.