If I believed much of what Mercola writes, I would probably want to stop being veg*n all together. Soy, in all forms, has its proponants and detractors. I, personally, find those who are maligning soy as the next asbestos to be a bit alarmist, but if you are terribly worried about it, you certainly can avoid it in your diet.
Lethicin, in general, is beneficial to our bodies, but I don't know if I'd go out of my way to eat pure lethicin, just like I try not to eat refined, extracted forms of any food. Whole foods are best, IMO.
Lecithin is found not only a byproduct of soy, but can also be derived from eggs & some other products that people often eat.
Just as a basic background on some of what lethicin does in our bodies, it serves many purposes including being an antioxidant. Lethicin is a mixture of fatty and fatlike substances and is produced by our livers, as well. It is needed by every cell in the body and is a key building block of cell membranes including the protective sheaths surrounding the brain. It also works as a fat emulsifier & is beneficial to cardiovascular health. Now that I am sounding like an infomercial :LOL ...