If an organiser wants to put on a race of this kind and if riders want to ride it, then it seems there ought to be no impediment to it. Clearly it isn't for everyone, but there are those who like to challenge themselves for whatever their own special interests are, whether climbing mountains, diving deep into the oceans, sailing or whatever floats their boats. If you are a cyclist looking for a challenge, the usual TT's etc don't fit the bill. Is it dangerous, does the event give other riders on public roads a bad name, is it lawful? All good questions, but living is dangerous with a 100% mortality rate and yet still humans go on doing it over and over again.
As long as the risks are known, I see no problem. Thousands are killed on the roads by cars and lorries every year, but driving goes on and no one is suggesting stopping it.