What a great topic! Here's my two penneth....
If you are a member of society, then you must morally abide by the rules of that society.
If you have a boat on BW waters then you need a licence and possibly a BSS.
On the roads I assume no one is defending not having a licensed, insured and MOT'd car. What is the difference?
The option does not exist to pick which rules you obey and which you do not.
As to the point that the boater is too poor to buy a licence...Well, if you see them give them a knock and offer them the money for one (I think cash would be prefered), and wait to see how long it takes them to display the licence.
The canals are not a freeloaders paradise, and I for one will report any boats I see without a licence.