Originally Posted by slowandsteady
I ride on 50 mph two lane country roads with no shoulder. If I were driving a farm tractor the driver of the car would have to wait until it is clear to pass. Why should a driver of a car be allowed to squeeze past me?
He shouldn't. But a bike is a lot narrower than a tractor. So there are often situations in which the road is wide enough that it is possible to safely pass a cyclist and leave plenty of room while doing so without going into the oncoming lane or taking up only a very small part of an oncoming lane for a very short time. Road widths do vary after all.
Believe it or not driving at 20 mph for a few seconds never hurt anyone.
I know that.

You're talking to a fellow cyclist here, whose biggest pet peeve might be impatient drivers - not to a JAM! If it were up to me, I'd place cyclists in the middle of the lane by default and have them treated as a full-sized vehicles.
However, we don't live in the world of my dreams, and I see no point in further aggravating impatient drivers when it is not necessary to do so. Especially when it's illegal. There is the whole trouble with the police that
Machka mentioned. I agree that laws prohibiting riding two abreast regardless of the circumstances are bad laws, but they exist and why give a$$holes a chance to legally harass you? If you wanted to prevent the motorist from passing unsafely, you can still do it, by legally riding close to the middle of the lane single-file.
And really, whether or not they need to use half of the oncoming lane or the full oncoming lane it doesn't matter.
In situations I'm thinking about, they don't need to use the oncoming lane at all if the cyclists are in single file. I can also think of situations when it IS safe to use a part of the oncoming lane and NOT safe to use the whole oncoming lane. And yes, I can think of a situation when it doesn't matter how much of the oncoming lane you use to pass. But you're trying to say that the first two types of encounters never occur. They do.