Now, I suspect I agree with the spirit of what he means. But I have an issue with how he's saying it. What does it mean for something to be terrible for the environment? I claim that the word "terrible", in this unqualified context, is subjective. Kind of like saying "Christianity is terrible for Canada".
Let me continue with a different example, taken from a similar debate I had with another friend years earlier. He said, "Sugar is bad for you." What does he mean by that? One interpretation is,
Compared to the host of other food choices we're blessed with, food containing refined sugar tends to have a higher glycemic index.
I expect that's along the lines of what he meant. But another interpretation is,
If given the choice to eat sugar or nothing at all, you will live longer if you eat nothing.
That, by the way, is false; sugar will save your life if you are severely energy starved.
My objection in this example is to the unqualified use of the word "bad". Last I checked, nature doesn't label things as good or bad. It's not written on their atoms. Consider a lion killing a zebra. Is that good or bad? Well, I suppose it depends on your perspective; it sucks for the zebra, and rocks for the lion. But outside of those perspectives, it's neither. Things just ARE.
If you want to use the word "bad", you have to qualify it with a purpose. That is, the lion killing the zebra is bad for the purpose of the zebra's survival. And it's good for the purpose of nourishing the lion's pride (social unit).
Getting back to "raising cows to eat is terrible for the environment". Again, the use of "terrible" should be qualified with a purpose. For example,
Raising cows to eat is terrible for the purpose of water conservation.
... terrible for the purpose of minimizing greenhouse gas emissions.
This takes the statement from a subjective judgement, to the realm of a specific and quantifiable claim.
OK, I can understand that some shortcuts are allowed for the sake of conversational economy; you might lose someone's interest if you take these technicalities too far. But for something as complex as the environment, how one factor impacts the big picture is anyone's guess. For those cases, a clear understanding of cause-effect is more useful than blanketing judgements. If nothing else, it cultivates an appreciation for how complex these issues really are.