Supply management is synonymous with products of unquestionable quality and human-scale farming.
It also ensures that farmers are able to pass down their farms. When the effect of a trade agreement is to pull the rug out from under farmers, they can't pass on their farms to the next generation. Do you think their children would want to take over the ailing family farm?
Supply management provides social and economic stability as well as stability vis-à-vis food security. That's what it does in Quebec and everywhere else in Canada, in my view.