Mr. Aitchison, fair dealing is a very common element of copyright regimes across the world, and the line as to whether it's 10% of a book or 20% of a book changes and so on and so forth. In many cases, the allowance is much higher.
It is to balance the users' rights and the creators' rights. It's to create an environment where students can learn so that in certain places there's free access to parts of a work. It's an important element of Canada's copyright law, just as it's an important element of copyright laws across the country.