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We Can't Be 100% Vegan, Why Bother? | Veganspeak
The main reason we find animal by-products in so many things is because of the scale of animal industries. There is so much waste produced from these industries (ligaments, bones, brains, intestines, etc), that it makes economic sense to use it elsewhere. Decreasing the production of animal products, by avoiding the main industries, would make the use of these waste products impractical.