Vintage clothing is one of the most sustainable ways you can purchase clothing. No additional material is being added to the environment, therefore no additional toxins are created that would’ve been during the manufacturing of a new article of clothing.
That being said, an important component of ethical vintage shopping is that a very large percentage of vintage clothing is not sold and subsequently shipped overseas.
The fastest moving vintage clothes are from higher end brands. There are plenty of vintage stores that only sell high quality clothes, but even more have fast fashion brands on their racks. If there continues to be demand, vintage shops will continue to purchase more.
Part of the responsibility in changing this is vintage shops themselves. If they don't sell vintage, consumers cannot buy it, which means some shoppers may not buy so much fast fashion knowing they won't be able to sell or consign it to a vintage shop.