What exactly do you think we should plan to do with all the grass and waste product currently being used in feeding animals?

Currently 75% of the product grown is for animal food. Grass fed is less than 10% even in the USA, and all give extra feed. Grass produces way more methane in ruminants compared to starch based feed like soy for which the rain forest is burned down.

and the massive inefficiencies that would introduce.

You know you need massive amounts of feed to others before you can kill them for your pleasure? We could feed 10 billion people with the product we grow right now. Instead we feed it other animals.

I argue it’s easier to find technologies that can mitigate and reverse emissions than it is to find technologies to let the world cut out meat entirely.

Others know it is not possible and act according: https://www.euronews.com/green/2022/01/31/china-includes-cultivated-meat-in-its-plan-for-the-future-of-food

https://www.iatp.org/ipcc-report-reveals-urgency-methane-reduction-need-reduce-industrial-agriculture

Which is absolutely your right. I have become convinced that my mixed diet leads to ultimately less death than a plant-based diet would

Explain that. A plant based diet uses less resources in every way. You don't think there are no animals killed for animal feed which is just a bad conversion of food, do you?

We all have a impact on the environment and on others, but acting worse than we have to because of a nirvana fallacy is not acceptable. While our impact on the future is hard to measure it is today when we decide to support killing and abuse or not.