British Columbia

Being vegan is recent fad or trendy thing from the perspective of world history.

Abstaining from animal products has been a thing for at least a couple centuries (see al-Ma'arri)

Nutritionally, veganism is not healthy without an extensive amount of supplements.

The only supplement you must absolutely take on a vegan diet is vitamin B12. The source of vitamin B12 in omnivore diets is also supplements, albeit given to the animals raised for slaughter rather than taken directly. Supplementing omega-3 is also highly recommended for vegans. The other ones you'll hear mentioned are vitamin D3 and iodine, with both of which many foods are fortified since most people, including those who eat an omnivorous diet, don't get enough of these through their food. This is hardly what I'd call "an extensive amount of supplements". I've been vegan for 7 years and the only supplements I take are B12, as well as vitamin D during the winter months since I live in a northern area.

Veganism is an opinion or philosophy, it does not come from any doctrinal teachings with historical writings to count as a belief system on the same level as someone who can only eat certified kosher food.

I agree, a person's carefully thought-out ethical decisions about what they consume are different from someone doing something because an old book tells them to.