That’s a common misconception that’s been passed around the Internet so long that it’s become common knowledge. There’s a great (now deleted, but archived) writeup showing that the Wachowskis always intended humans to be batteries. The actual source of the “processors” idea came from a Neil Gaiman short story written to promote the movie at its release

Ok but remember this part?

We have a number of options – some fall on the shoulders of consumers; some on producers.

Maybe we can’t convince everyone to quit eating meat, but I would hope that we could appeal to self-described environmentalists, who have a stated interest in making sustainable changes.

That’s the OP’s point, after all. That the science unambiguously states that we need to stop eating meat if we care about meeting our climate goals. Any environmentalist who learns that this needs to happen and still chooses to eat meat is acting against their own ethics.

It has to be both. Our World in Data puts it one way:

We have a number of options – some fall on the shoulders of consumers; some on producers.

Or to cut through the flowery language - farms need to stop producing meat, and people need to stop eating it.

The biggest reduction would come from the adoption of plant-rich diets. Emissions would be halved compared to business-as-usual.

Man I had to rephrase this a dozen times and I still don’t have a good way to communicate what I’m trying to say.

The goal of this kind of callout is to make vegetarians, people who already value animal welfare, aware that they may still be contributing towards animal cruelty. For example, I was a vegetarian for years and then got rocked by the realization that, “oh wait, vegans aren’t just crazies that I can blow off, it was me who was ignorant the whole time.”

So I anecdotally assume that a huge percentage of vegans are vegetarians who went from thinking “vegetarians and vegans are basically the same, besides vegans taking the idea too far” to “oh wait there’s a huge important difference between the two.” On vegan spaces, people often joke that “bullying worked on me lol” because the gentle approaches are easily ignored, but the really blunt “your actions don’t align with your stated ethics” is really difficult to brush off.