This post demonstrates the success of marketing "protein is meat". Such that when someone mentions reducing meat consumption, someone else thinks they are referring to a low-to-no protein diet.
Protein in terms of protein / calorie ratio of food tilts protein sources to meat and dairy. Easy way to compare foods and meals is to compare grams protein per 100cal of a given item. Things like meat, cottage cheese, yogurt, etc., top the charts.
So if you want to maximize for protein consumption without putting on fat mass, you tend to look for meat, dairy, and things derived from them (whey protein isolate).
The controversy is about whether humans need gargantuan amounts of protein.
Your post is assuming protein is very important, and thus it’s important to maximize protein per calorie.
The post you’re responding to is discussing the fact that any time vegetarian or vegan diets come up, people launch into criticisms that are based on the assumption that humans needs lots more protein than occurs in vegetables.
One issue I've seen when assessing some of the vegetarian or other plant-based diets proposed has been neglecting to account for protein. Most men at least don't enjoy the muscle loss associated with eating a low-protein diet, which is what the implementations I've seen often look like.
That said, Americans are predominantly overweight and obese. A diet high in protein but low enough in total overall energetic content is an excellent recipe, when paired with weightlifting and a few days of cardiovascular activity, for improving musculature and eliminating fat.
A scientific example demonstrating this point, entitled "Higher compared with lower dietary protein during an energy deficit combined with intense exercise promotes greater lean mass gain and fat mass loss: a randomized trial": https://academic.oup.com/ajcn/article/103/3/738/4564609
