It sounds like you already have counterarguments to those two points. Why not make them in a discussion instead of refusing it outright based on what you perceive as weak arguments? I'm not vegan and won't argue about the merits of these arguments, my only point is that it's unwise to refuse a discussion unless your opponent adheres to arbitrary rules you postulate.

As to your second paragraph, I think you're referring to a different commenter. I don't believe I made a point about believing something to be possible. Please do correct me if I'm missing something, though. I do agree with you here. Lab meat won't save the climate. But, to be fair, that wasn't your original point which talked about forgoing meat consumption altogether. Which I don't believe will happen since we can't even reduce car sales but it could definitely be part of a solution for climate change.