It definitely has to do with one's culture and upbringing. My wife grew up in a big family in Miami. Cooperative overlapping was (and is) their lingua franca. I grew up differently. My father dominated conversations and never gave the rest of us a chance to share our thoughts and feelings. So for me, cooperative overlapping brought up many of those feelings from childhood of not being heard. My wife, however, is not overbearing as my father is. She means well, whereas he often did not. Drawing that distinction helped me start to change my stance on her cooperative overlapping.

My one exception is when she doesn't know where I'm going with my line of thinking. She ends up jumping to the wrong conclusion. In this case, she is interrupting. It sidetracks me and disrupts the flow of conversation, instead of building on what I was saying.

How people feel about cooperative overlapping seems to be akin to how people feel about personal space. Different cultures have different thresholds for personal space. One person's too close is another person's just right. Too close may seem rude to one person, but too far may feel distant and withholding to another. But people aren't actively trying to invade another's space or keep others at arm's length. More often that, it's just different sensibilities. I think understanding that is key to reaching a compromise.