Personally that justification is based heavily on the taste.
I personally wouldn't eat meat if I had a good alternative. I rarely do, I eat it for health related reasons, considering my setup.
Everyone who treats plant-based diets with any degree of responsibility will stress the need to plan them carefully, considering the needs of the individual and their stage of life, and to accompany them with supplements to make up for the nutrients that not even well-planned diets cannot provide.
For example, "Top Tips" from the British Dietary Association:
* Carefully planned plant-based diets can support healthy living at every age and life stage
* Plant-based diets can help to manage weight and may reduce the risk of type 2 diabetes and other chronic diseases
* You can get all essential nutrients from plant foods but vegans need to ensure a reliable source of vitamin B12
* If excluding dairy, make sure you consume other calcium-rich foods
* Include a wide variety of plant-derived foods to ensure your diet is balanced and sustainable
https://www.bda.uk.com/resource/vegetarian-vegan-plant-based...
Far, far from "just buy some beans/lentils". TBH that's just irresponsible and dangerous advice.