Oh, the irony. Richard Fries' article starts with this quote:
“We have met the enemy and he is us.” --Walt Kelly, Pogo
Indeed. Look at that photo of that group. Fries' caption refers to these cyclists as a "large, unruly group". But let's take a closer look!
See the guy in the very back, in the half-red/half-blue jersey? Now imagine he's the only one on the road - all the other cyclists are gone. Do you think that car can safely pass that cyclist without crossing the double-yellow line. NO WAY!!!
To safely pass, even cyclists riding single-file as far right as our red-blue guy, cars must be driven over the center line.
Now, once it's determined that passing motorists have to be driven over the center line, they have to make sure that the oncoming lane is clear. This is true regardless of whether they need to use the oncoming lane partially to pass far-right cyclists, or to use it full to pass a "large unruly group".
Finally, say there are 40 cyclists. Riding single file they are 40 cyclists long. Riding 4 abreast, as they in this photo, they are approximately 1/4 as long - much EASIER to pass!
How is that unruly?