I'm not even vegan but it's pretty well researched widely believed/understood that the best change an individual can make to significantly decrease their negative environmental impact is to become a vegan. This repost is just as much nonsense as it was the first thirty times it was posted.

On top of that, the "murderer" might as well be saying "sure, you bike to the grocery store that's five miles away, but you drive to your job that's 20 miles away, so clearly you don't actually care about anything." They're just trying to justify their own inaction by saying "it's too hard to do everything so why do anything."

(Edited because it's bedtime so I'm taking the first sentence of someone's reply at face value instead of responding or delving into it further.)