I agree.
Australia is the only country to go free market. It removed all subsidies to dairy farmers in 2000. The result: the number of dairy farms  went from 12,000 to 6,700 in one decade, and farmers are suffering.
Professor Bruce Muirhead, at U of W, specializes in agriculture policy, and supply management specifically.  He points out that there is little room for exports by Canada anyway, almost all dairy production around world is consumed in countries that produce the milk and cheese.
"Every critic of supply management huffs and puffs about the international opportunities we are missing because of our made-in-Canada system. They don't seem to realize that only seven percent of total global dairy production is traded internationally. And NZ already controls about 33 per cent of that seven per cent -- it doesn't leave much for everyone else! Clearly, 93 per cent of dairy production in all countries stays at home."