I have first hand experience with someone in my immediate family who was unable to sustain a vegan diet. She became anemic and was ill 6 to 10 times a year. Iron supplements did help, but only enough to bring levels up to the lower bounds of normal. This went on for years. After reintroducing some amount of animal protein, her health and iron levels improved dramatically.

If you want to change someone's mind you could be less condescending. Right now, you are acting like the arrogant vegan stereotype. Do better.