you don't have to.
you can buy a lower quality bag for less and have a fraction of the product. less longevity, less enjoyment, less practicality, less ability.
you can though... in fact anyone living in america who uses a cycling backpack daily should be able to budget a mission workshop bag if they work hard enough.
300 ain't that much money if you don't have car payments, debt, or bad habits. a lot of us do, and that's okay too.
just don't complain about spending 300 on a bag that is worth it. these are worth it. not so much for some other bags, regardless of where they are made or if the workers making them are treated fairly.