Maybe it's a universal truth that arguments create fixations in the minds of people, and agreements get you to move on to the next topic. The last thing you want to do is let a cantankerous person be fixated on something you need him to move past. So agreeing with him will make him let it go.
Sometimes when people want to avoid the important things you've come to talk about, they'll bring up something controversial to bait you into an argument. Why? Because they know the longer you spend in fixation with this, the less time you'll take on the next subject // the subject they don't want you to get to.
Knowing how to avoid arguments, keeps you in control of the conversation.
A good example of this comes from the legendary Dale Carnegie: How To Win Friends & Influence People.
"Mr. O'Haire became one of the star salesmen for the White Motor Company in New York. In his own words: 'If I walk into a buyer's office now and he says: "What? A White truck? They're no good! I wouldn't take one if you gave it to me. I'm going to buy the Whose-It truck," I say, "The Whose-It is a good truck. If you buy the Whose-It, you'll never make a mistake. The Whose-Its are made by a fine company and sold by good people."
He is speechless then. There is no room for an argument. If he says the Whose-It is best and I say sure it is, he has to stop. He can't keep on all afternoon saying, "It's the best" when I'm agreeing with him. We then get off the subject of Whose-It and I begin to talk about the good points of the White Truck.
There was a time when a remark like his first one would have made me see scarlet and red and orange. I would start arguing against the Whose-It; and the more I argued against it, the more my prospect argued in favor of it; and the more he argued, the more he sold himself on my competitor's product.'
Mr. O'Haire and Dale Carnegie realized that the person who uses argumentative bait, controls the conversation, until you walk right past it. Once you've left it behind, you can begin to talk about the important things again. Now YOU'RE back in control again.