There was a much-publicized case in the UK not so long ago - last year I think - whereby a Messenger cyclist knocked down a pedestrian and killed her. He's in prison now. Just this week a CCTV image was posted looking for another Messenger after an elderly man was killed too. It is a highly competitive business as the Reporters delved into what happens once these type of cases became more widely reported, the guys and girls involved do take it very seriously, there is a huge amount of competition as they go about their business in crowded cities, running red lights, ignoring all traffic rules and norms in their pursuit and, putting pedestrians and other cyclists at great risk. There are annual races too, no sanctioning body, very illegal etc that takes place in Europe.
All that said, I'm sure not all are like that. I'd absolutely agree too that the best of these riders have a high degree of skill - akin to that of any good off-road cyclist where significant obstacles present themselves. They may not win any track races, time trials, crits, road races, XC MTB etc but they are good at their own niche and while not an officially legally sanctioned division - as far as I am aware - it is competitive and it is sport. Not for me however, I don't care for having to break the law in order to win since I would stop at traffic lights etc and not risk pedestrians well-being. Perhaps on a closed circuit well Policed and no risk to others, then yeah, I'd give it a go, could be fun - as a road sprint specialist and XC MTB'er too it would suit me.