I was raised to formulate my own opinion and to be able to defend that position. That by defending the position and listening to other's reason's for their position, it would help me to find out if my position is accurate or not. Maybe someone else will show me some fact that I was not considering in my position that would allow me to change my opinion. At no point do I have to agree with the other person until they have convinced me that their position is superior or equal to mine and then I can consider what they are saying.
An example of this would be Ron Paul's position on the death penalty. From what I now of Ron Paul, he has maintained a pretty consistent position on the role of government. He has been able to keep this position for many years because he has a solid basis for his position and nobody, as yet, has given him a superior argument for him to change. One area where he admits changing is his opinion of the death penalty. Previously he was in for and now he is opposed as he says he has heard convincing arguments to encourage him to change.
The advice from Dale Carnegie and Howard McDonald is to agree with everything other people say, even when they are wrong. The idea is that, we might be wrong, so by saying they are wrong we might be the one's who are wrong. Sort of like the idea of it's better to set 100 guilty people free then put 1 innocent person in jail. Also, by resisting the person, they will resist us and be less open to hearing our position. People, including me, seldom like being told they are wrong, they prefer the idea that they found out some truth on their own.
I guess that is a key, that people, including me, prefer the idea that they found out the truth on their own, rather than being forced to see the truth.
My reaction to that statement is something like, "But with all the wrong thinking in the world, how are they going to know they are wrong if I don't tell them?" As Dr. Phil would say, "How's that working for you?" How many people are convinced of my positions by me telling them how wrong they are and how right I am? I would guess very few, if any. It does feel good to show how many holes people have in their positions. I am valuing my ego boost over the good will I could generate by being agreeable.
What tool can I use to allow me to not only bite my tongue, but to agree with opinions that really get my dander up? Best I can think of is just to tough it out, bite my tongue and if I can't think of a way to agree, then just keep quite.