Just because a point is factual does not make it worth discussing or mentioning in an interesting convo. If everyone stopped driving a 1-2 ton personal metal brick on wheels and started biking climate change would also be slowed, or if half the population died right now it would also be slowed, or if the sun exploded. Who cares? These are not realistic solutions to that problem so what is the reason you would bring it up when discussing diets? Is the reason to inform? It just seems to me like someone mentioning "murder" and "if no one ate meat" while discussing diets is not looking for useful conversation.

You mention the difference is in believing it to be possible. I believe that meat harvested from slaughtered animals will someday be a rarity, but not soon enough to be (part of) a real solution for climate change. Lab meat is just now hitting consumer stores, and climate crisis is on our doorstep.