Years ago I used to water ski on rivers. Great fun - feeling of speed - obviously never did it with passengers on board, just on the way back from charters when I had an empty aeroplane. Or sometimes I'd just do what these guys were doing - follow the rivers at twenty feet looking for crocodiles.
Then one day I thought - what happens if the engine stops? I can pull up to about three hundred feet if I'm lucky. Just time to choose where to crash. No VHF contact low down and probably no time to get anyone on the HF. End up probably dead, certainly hurt, and no one would know where I was.
What they are doing isn't clever. It isn't cool. In a single engine aeroplane it is incredibly stupid. That's what I decided twenty odd years ago and nothing I have done in an aeroplane since then has changed my mind. If you don't agree then think about it. It isn't the same as an organised event like red bull with paramedics and helicopters on the scene just in case.