A reader, Lawrence Cohen, said that he always paid for a full-fare first-class seat. His preference for an aisle seat in the front row of first class is so strong that he will shop around for other flights if he can’t book that choice on a particular flight.

Mr. Cohen wrote to me last week saying that about 25 percent of the time, he is asked to swap his seat to accommodate people traveling together, even though those people are often upgrades to first class traveling on cheaper coach fares. He wondered whether there was any consensus on the “etiquette” of responding to such requests. I’m passing along the question to readers.

I use the word etiquette because in my opinion most frequent fliers practice civility toward fellow travelers. So, in my experience, a family with toddlers in coach, for example, can usually depend on other travelers to offer to switch seats willingly to accommodate them if they aren’t sitting close together.

In a telephone interview, Mr. Cohen said that he thought that some people traveling together on leisure trips exhibited a “sense of entitlement” about being able to sit together. He recalled a recent flight on which a woman sitting in the aisle seat across from him was badgered into giving up her seat and moving a few rows farther back by a couple who insisted on sitting together. The flight attendant also told the woman to swap, and thus “became a tool of this couple to get their way,” Mr. Cohen said.

“My problem with that particular circumstance was, why was it that this couple apparently seemed to think that their preference as a couple to sit together outranked this single person’s preference?” he asked.

Back in coach, the issue comes up frequently. And some recent media accounts have taken a tone of outrage. Here is how the situation was framed by a headline in The Daily Mail, a London newspaper with a growing online presence in the United States: “Plane Greed: Airlines Charging $25 Just for Families to Sit Together.” And in Washington, Senator Charles E. Schumer recently received copious publicity by denouncing the airlines for “requiring parents to pay an additional fee to make sure their kids are sitting next to them.”

Well, you could put it that way, but you would be pandering to those who don’t really understand the new realities of airline fare and fee structures. So-called ancillary fees, including checked-bag fees and those for things like the less-awful seats in coach, accounted for about $12.5 billion in extra airline revenue on big airlines in the United States last year, and a total of $32.5 billion worldwide, according to a report by Amadeus, the global reservations system, and IdeaWorks, the airline-revenue research firm. For many airlines, ancillary fees, not base fares, are the difference between profit and loss.

To Mr. Cohen, the issue is fairly simple. “I like to be able to select my seat, so I’m willing to pay up for that,” he said.