I mean, if we're looking at the graphs, beef really is the only "offender" (if you can call it that) and only in the current consumed amounts. If people ate a lot more chicken and less beef, the GHG effect from animals would be lower than the same number 500 years ago due to animal population culling and advancements in agricultural methane reduction.

At that point, the term "negligible effect" becomes unreasonably harsh. Even with the worst claims against the effect of livestock on the environment (many of which we might not see eye to eye on), it's simply objectively not an environmental issue if people are eating chicken and some pork as their staple proteins. You can call it an animal rights issue if you want. Considering chicken is almost objectively a correct and healthy food to eat, two thirds of the diet triforce (health, environment, animal rights) become non-issues.

And the cool thing, even if I disagree with the outcomes it's healthier for us to eat a bit less red meat as long as our meat protein intake stays reasonable from white meat and seafood.