Riding in a group takes discipline. I’d agree that big groups are just counter-productive in that they p*** other road users off. A group of around 8 – 12 is ideal, any smaller and you don’t really get the benefit of being a group – drafting, etc., any larger and it’s hard to keep things under control.
There’s so many variables about when and where you should go single line both for the safety of the group and for the convenience of others, which are often perceived to be at odds with one another.
There’s a wide variation in the ability of cyclists to ride in a group (I’d put myself somewhere in the middle – still a lot to learn), the worst group rider in our club is from a mountain biking background, he just can’t ride in a group: inconsistent speed/effort; riding against the flow of the group. We’ll get him in to shape, even if the air turns a little blue!