your opinion is... wrong

[GSNW]

A polite discussion of differences is really dependent on the people involved.  I have a relative whose views on social, religions, economic, political... etc... issues differ radically from my own, but we really love to hash out details and debate when we get together.

Instead of slamming them with the "your opinion is unsupported etc" response, you could politely inquire about the source of their "facts."  As in, "Oh, smacking yourself in the foot reduces your chance of foot-in-mouth disease, really!  Where did you read that?  Where was this study performed, under what circumstances, etc?"  I don't think that kind of inquiry is rude. 

I DO think it's rude when people state an opinion as fact and then get annoyed when anyone wants to contradict them.  If my opinion isn't up for discussion, then I don't *discuss* it. 

[Twik]

A polite discussion of differences is really dependent on the people involved.  I have a relative whose views on social, religions, economic, political... etc... issues differ radically from my own, but we really love to hash out details and debate when we get together.

Instead of slamming them with the "your opinion is unsupported etc" response, you could politely inquire about the source of their "facts."  As in, "Oh, smacking yourself in the foot reduces your chance of foot-in-mouth disease, really!  Where did you read that?  Where was this study performed, under what circumstances, etc?"  I don't think that kind of inquiry is rude. 

I DO think it's rude when people state an opinion as fact and then get annoyed when anyone wants to contradict them.  If my opinion isn't up for discussion, then I don't *discuss* it.

Unfortunately, it sounds like the OP is dealing with someone proselytizing for a scientifically unsupported theory that could endanger other people. These sorts will likely respond to "Dr. Wonderful, whose book you all should read, has DOCUMENTED PROOF that eating cardboard cures cancer, allergies and ingrown toenails. That's why you should all start eating nothing but cardboard from now on." You may know that Dr. Wonderful (doctorate from an online diploma mill, by the way) handily confuses anecdotes with documented studies, but trying to prove that it in social discourse becomes futile.

I think the most polite, yet firm, position is, "I cannot disagree with you more, but I don't think this is the place to discuss it."

[veryfluffy]

What's bothering me about this is probably a semantic problem: the difference between an opinion and a belief. Many people believe things for which there is no factual evidence, or which is contrary to the factual evidence that is available. Beliefs (eg that the Earth is flat or that drinking green tea prevents ingrown toenails) like that are neither valid nor invalid, so long as they do no harm to anyone else. In the OP's example, "eating ice-cream cures cancer" is a belief, not an opinion.

An opinion implies an assessment of facts or experience, or may be value-based.
I don't see how, logically, an opinion that is factually incorrect can be valid. "In my opinion, Skakespeare's plays are written in French" is clearly wrong." However, "In my opinion, Shakespeare's plays are trite, poorly-structured, and historically irrelevant", while possibility a minority viewpoint, can be argued with but is not objectively wrong. "I find Shakespeare's plays really boring" is a valid opinion, and can't actually be contested.

[LilacRosey]

I think its rude because sometimes people have opinions and they matter a lot to them and it doesnt matter if they are right to them it just matters. But I'm soory you have to deal with it because it seems you have strong opinions that matter to you too

[mmswm]

PS. Vanilla is WAY better than chocolate.

I totally agree!

Back to the actual issue, I've been having trouble with this issue myself.  Heck, I've been having trouble with a lot of issues, which is the reason I joined this forum.  When it comes to something as simple as food preferences, we have a saying in my family: "Don't yuck my yums".  This started as a way to teach the little ones not to be rude to people who eat foods that they don't like, but it's morphed into a catch-all for any situation where there's a simple difference of opinion on something relatively trivial.

As for more charged situations like medical treatments, I can be a bit heavy-handed, since I've dealt with a LOT of doctors (three high risk pregnancies, 3 preemies, 2 kids with a rare genetic bone disease and no consensus in the medical community on the "right" way to treat it will do that to you.)  I'm still working on how to be a bit more polite in these situations.

[Kaypeep]

You can always quote the late NYS Senator Daniel Moynihan, who said:
"Everyone is entitled to his own opinion, but not his own facts. " 
But I don't think this is going to shut down the opinionated quack who thinks cancer can be cured by delicious dairy desserts.

For someone like this, I'd bean dip them and not waste my time.  Nothing you say is going to alter their point of view.  I'd go with something like "Oh, there are so many points of view on the best way to treat cancer, we could be here all week debating them all.  Plus, I'm not a doctor nor do I play one on TV, so let's leave that subject to the professionals, shall we?  Now, what I REALLY want to know is, what is your darling son/daughter/dog/cat going to dress up as for Halloween?"

[Iris]

I was actually going to post a topic about this issue, so thanks for that!

I used to react similarly to you but eventually I realised that I never, ever changed anyone's mind and was just stressing myself out to no end, so I went with the bean dip approach. Note that I never, ever say anything that could be construed as support for these 'wrong' opinions. Now I have the problem that my exposure to insane ideas has greatly increased and THAT is stressing me out. I was hoping someone could provide me with a line between bean-dip and unfruitful arguments. I have to say "I cannot disagree with you more, but I don't think this is the place to discuss it" sounds good. Has anyone had any luck with that?

[jayhawk]

Or as my DH says, "Opinions are like---holes; everybody has one."