It was Twitter. This medium has improved my life beyond measure. Without it I would know even less than I do now (barely possible) and have even fewer opinions.
I had no idea until Twitter spread to the ranks of true celebrity that people had such difficulty selecting a breakfast cereal.
But on the serious issue of training on the roads, it does make me slightly nervous at times that people do it. I do it (alone and with my middle child - who races). When you are head-down and working hard, there is a marginal increase in the risks being taken. I do not think it significant enough to stop me doing it - a tiny incremental risk added to an already-tiny one. But there is a greater risk.
There was a stupido-massimo post many months ago on this forum from a member who'd been on another rider's wheel in a chain gang and had swerved when the rider in front braked heavily. He was asking advice about seeking compensation from the council, as he's swerved into a drain cover and crashed.
I thought at first it was a comedy post... but no. Worse still, he was being advised to go for all he could get.
Such people are in a tiny minority, but while they are out in chain gangs, there will always be a slightly spiked risk in training out on the public highway.