When I was reading the material in this section, I noticed about 250 deaths a year in small vessels were attributed to pleasure activities or pursuits. I would imagine that the majority of those were private owners and operators of vessels, and not people running licensed river rafting, canoeing, and kayaking operations.
Yes, it is a risky activity, and as you quite correctly point out, the risk of drowning or of sustaining a head injury exists, but the insurance people I spoke with this morning said they have far fewer claims of this nature. Given that there's an informed consent verifying that people are aware of the risk and that the guides and operators are trained, are running routes that are reasonably well known to them, and are trying to avoid demonstrably unsafe conditions, that would suggest to me that this is a balance of risk.
People want to do this kind of thing in society. We can legislate them out of existence by imposing extremely high insurance rates on them if you want to, but that will also mean that we will lose an activity that many people find pleasurable.