Never fear. The Government will take care of everything. Mandatory licensing and insurance, higher taxes and onerous regulations will put cruising out of reach for all but the most wealthy. Problem solved.
I agree with you that government legistlation is the way to go. I have my official Canadian boat operator's card and it means nothing except that I passed a multiple-choice test. On the other hand, I don't think it makes any sense to have the government decide who is capable and who it not - how are they to know the expertise level, common sense, and toughness of those going offshore?
There was a lot of fuss about Laura Dekker, the Dutch teenager who wanted to sail around the world. The Dutch government even took her into care for a year (out of the parent's control). We crossed paths with her this year and she very centered and a very capable and was doing just fine. What would saying he had to be 18 or 21 do? You would miss the well-qualified 17 year olds and allow any fool who is 22 (or 55) to jump right in.
Ultimately you have to rely on the responsibility of the individual - not something that people are used to in our society, but the sea has been setting the rules a lot longer than current attitudes about no peanut butter at school have existed. I know if you want to head off towards the North Pole or do similar treks in the far north you have to put up a bond to pay for SAR - I guess this is a form of insurance not for the individual but for the society. Not sure how it would work for sailors (or even if I believe in it), but at least it would mean that everyone is not responsible for the bad decisions (or even just bad luck) of the individual. I know when I head offshore I don't want to give up my EPIRB and be totally self-reliant, but I am not putting other demands on government/society like for roads, schools, health care, although I still pay taxes toward those things.
It is a really complex question, but I think it has to start (but probably not end) with the individual taking responsibilty for their decisions and, I agree, we should be saying to people that they should just buy a boat and go - unless we also tell them to not take an EPIRB, sat phone, or anything similar that would call for help.