You make some good points. However, there is a bit of inherent hypocrisy: every single captive-bred garter snake on the planet - in fact, ever single domesticated animal - at some point in history was a wild-caught. Whether the snake's mother, grandmother, or distant ancestor, at some point in their family history there is a wild-caught animal. So unless we're supposing that all trade in snakes cease and desist, we're still right back where we started from: someone had to collect those wild-caught specimens in order to breed them.

In some cases, this might turn out to be a good thing. Take for example the San Fran: due to habitat loss, the snake is nearly extinct. But because someone captured a few, bred them, and shipped them overseas, at least there are some still remaining. Who knows? If California enacts procedures that might help restore the SF's habitat, there might be opportunity for some of these captive snakes to be allowed to reinhabit their once-lost environ. Does this make it okay for someone to take them now? Not if it will severely impact the local breeding population, which, with an endangered animal like the SF, it almost certainly will. But what about with a T. s. sirtalis, whose habitat ranges all the way from Florida up into Canada? These guys aren't going extinct anytime soon.

Captive-bred animals: at some point, they had to be taken from the wild.