A Question for Catholics

I'm not a Catholic, so it's entirely possible that I'm just misunderstanding the nature and import of Laudato si'. Can someone help me out here?

My understanding:

While papal encyclicals are not automatically and necessarily ex cathedra, they can be. As Pope Pius XII put it in Humani generis, "[I]f the Supreme Pontiffs in their acts, after due consideration, express an opinion on a hitherto controversial matter, it is clear to all that this matter, according to the mind and will of the same Pontiffs, cannot any longer be considered a question of free discussion among theologians."

In Laudito si', Pope Francis doesn't just throw around some opinions along the lines of what kind of pizza he prefers. He goes on for 45,000 words, he anchors his opinions on various issues in the teachings of the Church and of previous popes, and he very specifically states that the encyclical is "added to the body of the Church's social teaching." That sounds pretty dispositive to me.

Now, a lot of non-Catholics are criticizing the encyclical's content on scientific and economic grounds, and I can understand that. But I also see a number of Catholics doing so as well.

Given the doctrines related to the infallibility of the Church and the pope's similar infallibility when speaking to/for the Church in an authoritative way, why the dissent? Doesn't the choice for Catholics come down to "accept the Church's doctrines or leave the Church?" If not, what am I missing?