Plus that a lot of people have no idea how loud they talk when they are on the phone.
I've already addressed this a couple of times now. For my example, just assume that the person actually is talking quietly.
But that doesn't address the other half of my answer which I think is the more important one, nmely, that hearing only half a conversation is a lot more distracting than hearing a full conversation.
This is not a universal thing. I can ignore people on a cell phone that are talking at a normal volume just fine. It's not an excuse to call people talking quietly and/or at normal volume on the phone rude. They aren't rude. They are talking just like everyone else nearby.
There have been studies (posted earlier in this thread) that show that for most people, half a conversation is more distracting than a full conversation. And for me that is definitely the case (shared office for a couple of years with a co-worker who was on the phone a lot for his job).
Yes, and I responded to the study stating that the study is not universal. It is simply a study. Does it hold some truth? Perhaps it does, for some. Not everyone.
Why should a person who is speaking on a cell phone at a normal volume just like everyone else have to stop their conversation, while everyone else is free to continue theirs?
As someone who argued for the other side upthread, I thought I'd give my reasoning here, which readers may reject or approve of: the problem I see is that despite our best intentions, humans have an attention capacity that is limited in certain ways, and verbal inputs demand more attention than other types. So when someone's on the phone, they may respectfully make an effort to maintain an acceptable volume and sustain it for awhile, but the truth is it is difficult to fully gauge whether the tone of voice you're using is "normal" as regards your environment if you are hindered in being able to pay attention to your environment. The Dear Abby letter is a case in point, where someone thought they were the paragon of civility, to the point where they repeatedly ignored pointed evidence to the contrary.
What you've said is unassailable if we're talking about situations where the surroundings permit it--i.e., there is already other noise. But these are also non-ideal situations in which to use a phone, so it's not the arena in which the behavior starts to grate and become an issue. For me (and we've established I'm high-strung earlier in the thread

), it's the basic "to heck with you" sentiment implied by entering a quiet place like a 7 am commuter train, seeing that everyone else in the car is reading or concentrating on something else, and nevertheless squawking into a device 2 feet away from everyone. I also think that having an in-person conversation at high volume in a quiet place is a little disrespectful, but I also differentiate between running into or travelling with a companion, and making the conscious choice to use a phone. Maybe people like to take advantage of quiet situations to use a phone (naturally, right?), but to me it's a problem when the quiet situation so conducive to phone use has other captive participants who wish to also take advantage of the quiet. Then again, I tend to speak in a low voice anytime I see that I am near someone reading or if the general volume level in a room or situation is low; maybe this is why this bothers me this much. Maybe I need to loosen up...
I'm not advocating a blanket declaration that this is boorish; it is often necessary, and like Dotty G said above, there are tons of behaviors that are potentially distracting. However, this specific, avoidable behavior is becoming widespread enough that I would just to implore people like the Dear Abby LW who, daily, use their commute to make nonessential phone calls to consider the other people who, daily, are stuck listening to them.