Yes this policy helps some rural families, but it also condemns all the other rural families to getting only variable quality, intermittently available, expensive dairy products. Every protectionist support for a local industry imposes a cost on everyone else, to the point where everyone benefits a bit from protection, but also pays costs on all the goods and services they themselves consume. It may even be sustainable, but only at the price of sacrificing the chance of a better future.
Change is painful, no doubt about it, but opening up to international markets can also mean opening up to international investment, technical skills and partnerships. It needs to be coordinated and there should also be transition plans to mitigate some of the pain. I do believe it’s for the best though.
(No value judgement on your position though, I generally think that this treaty is a bad thing due to its role in expanding China's power and influence, when it should be contained.)