I think it is usually a good thing to express honest disagreement, but in a rational discussion, we should treat each other respectfully and respect each other's right have their own views. And it also good to remind ourselves at times that no one has a corner on truth, and that all each of us have is our own world-view, when it comes down to it. I do also agree that people should tolerate honest disagreement, as long as the other person is respectful and doesn't behave rudely or attack you.

I often preface my opinions with "This has been my experience" or "This is how I understand this issue". That is how I let people know that I am not insisting "that I am right and others are wrong." This approach can prevent the disagree-ers from getting angry and defensive.

If i am going to offer an opinion in these occasions I start by saying i listen to all views to evaluate and perhaps change my view. In your case I challenge your facts,premise,methods etc and then present my view.

I shut the fuck up, smile and move away (in case I can't control my laughter)

I don’t agree with a lot of opinions. But I try not to be mean or rude in my responses. It is difficult when you are communicating through a text based forum, as emotion and context can be hard to establish. Sarcasm and humor are examples. Attacking someone, because of an opinion is just wrong. Especially if you are asking for opinions.

I run into this a lot in my jewelry and other crafting groups. They will post a picture of their creation and ask for opinions. What they really want are only positive comments. They do not want to hear that I do not find their crap visually attractive, or that they have mistaken a rock/mineral for a similar (this is actually a huge problem, they overcharge for a common agate [or other rock], claiming it’s some special rare piece, it’s infuriating to know they do it and do not care they are ripping off customers), but much cheaper one, or even that it is wrong somehow. I will be attacked for saying I don’t like it. I respond by saying to not ask, if they don’t want real opinions.

Sometimes I just like to piss people off or see the look on their face. I have a general lack of respect for humanity as a whole. Some individuals I like and respect, but not that many.

Everytime I assert an opinion, I consider the possibility it will be attacked, one way or another, and I tell myself that it is simply my opinion; it may or may not be reflective of the absolute truth, or may be somewhere near truth, or perhaps only truth as I see it, and anyone is free to express a difference. I do not invest myself to the point that I let it bother me. To another person, their opinion is just as valid as mine even if contradictory.

Anyone who thinks their opinion is worth more than the next person's, needs to remember the old saw, "Opinions are like assholes, everybody has one, and they all stink."

I just keep my cool and act like there not angry or ignore them or block them.

As far as I'm concerned, we're all entitled to an opinion on any subject - and we're all entitled to respond to other people's opinions with our own. However, there's a constructive way to do that, which is different to attacking; a lot of people could do with learning that difference.

If I can, I try to steer away from the topic if it is not necessary. I work as a programmer, so sometimes how to approach a problem is something you have to defend or relinquish on. Best thing to do for yourself is learn to let go, especially if this person isn't really involved in your day to day life and is not harming you.

I see that some people have a complex where they have a poor way of dealing with opposition. I see it in gamers. SOme can take a loss very well. Others throw temper tantrums.

I usually load up on facts and destroy them.

Good question

I've run into this too. I'm sure all of us have (and probably still do) believed in "old wives tales" that we were taught before critical thinking kicked in. Most often, when I repeat such a thing, I will be met with nodding heads from others, who bought into the same thing. On occasion, someone who knows better will ask me why I believe that and occasionally offer evidence to the contrary. Which is embarrassing but eventually appreciated.

But on rare occasion, someone who knows better will attack viciously, hurling ad hominems before offering evidence. That goes beyond embarrassing into the tramatic and is totally uncalled for IMHO. I still don't know why some people feel they need to react this way.

After all, we are all born ignorant. It's a life long struggle to overcome it.