Please note that Veg*n is a common terminology for vegetarians and vegans cause typing out vegetarians and vegans 30+ times is exhausting. I presumed that because you said you generally avoid eating meat you fall into the category.
The point is the sanctimonious attitude isn't welcome and is utter nonsense and garbage and often misinformed. For example, you, uh, might wanna check your facts on beef numbers. Mainstream beef is substantially less than 500 gallons (granted much more than avocados).

And it completely ignores the fact that avocados are grown in a low water area that promotes crime and poverty for whole swaths of underprivileged native people whereas beef production tends to provide a higher take of the profits to their farmers because of it's luxury status and can be grown on non-crop-arable land.
So you can say "Avocados are better, plants are better"... But they often aren't a good option for a LOT of people and for many poverty-stricken farmers beef is much more reliable. Much like I doubt that being carless is a good option for you. Even though being carless is better. After-all, a quarter of the worlds emissions are from cars. But I can't expect you to have no car and lose your income for it just to save on emissions, that would be horrible of me.
Other people might still be eating meat, but doing other things to change their lives, but the majority of the types of threads the OP are talking about aren't interested in that. They don't care that their avocado comes from impoverished regions of south/central america, that their bananas feed a totalitarian system in south america, that their agave syrup kills bats natural habitat in mexico... The sorts the OP are talking about don't care that the people they're talking to are usually already raising their own food, and eating locally, or hunting sustainably or drying laundry outdoors, or running solar panels, etc. countless other positive changes. They DO care that someone ate their OWN bird on their OWN property and that's a Big Bad. And that sort of the problem.
The problem isn't with doing something to try to be better. The problem is with considering your way the objectively best way and then, additionally, expecting other people to do the same. And this is a common problem for small farmers dealing with veg*ns, and it's a problem on this forum even in the meat birds section.