Welcome to the board. It is a great support network for responsible snake keeping.
I have a few thoughts, but please excuse me for being a little bit less than organized...
Sometimes I feel that way when I go to a zoo.
But most zoos take very good care of the animals (as stated above, they are given a better chance at a longer life with a scientific level of care) and they give so many many people the opportunity to gain an understanding, appreciation, and love of animals. I see that nice fat Polar Bear at the Lincoln Park Zoo... he's a lot better off there and I and wonder why humans aren't doing more to protect the global environment. If each person who sees that bear uses one less plastic bag per day...
Also, I think you could ask the same question about all pets. But no one questions dog ownership, horseback riding, dairy cows, wearing wool... Snakes/reptiles haven't been domesticated as long, so I guess they are targets for this issue.
Do they not have enough of a "purpose"? But why do people have cats? Companionship? Hold a snake and tell me that little guy isn't a good companion.
I know that, unfortunately, you can't say this about all pet owners, but I do think that the bulk of us have a respect for nature and desire to promote that value.
The reason I got my pet snake was two-fold:
1. It would not be a responsible choice to have a more traditional pet - I don't have a lifestyle suited for a dog.
2. I want my children to appreciate and care for animals. I want them to grow up with respect for the beauty of nature.
HTH.