The HSUS and PETA are pretty much in control of the law makers there when it comes to animal-related law. I'm honestly surprised that cats and dogs are legal, but then, there have been two attempts to force mandatory spay/neuter of all cats and dogs over the age of four months, statewide, ignoring the huge upsurge in shelter uptake and abandonments wherever these laws have been passed locally, so the effort is at least underway to prevent the breeding and selling of those animals within the state of CA, for their own good, of course.
Not to side with PETA (the HSUS does good work and isnt comprised of crazy people), but I would support mandatory spay and neuter laws unless you have a breeding permit. Domestic cats and dogs are some of the most damaging invasive organisms the world has ever seen, and we do not need any more of them running around.

People cannot actually be trusted to make good decisions on their own unless forced or given some sort of incentive. This is the reason we have abandoned animals in the first place, or "house cats" which are let out at night which decimate bird and lizard populations.
Now, to be fair, there are a lot of states back east where it's illegal to own NATIVE snakes, including Georgia. You can't have a Water Snake there, or a Corn, or a Chain King, or an Eastern Garter or Ribbon, not even a captive-bred morph.
You have a copy of the legislation there? In most states that have such laws there is an explicit exemption for captive bred animals.

It's like an insidious cancer, really.
Why? To play devil's advocate, there are a lot of species (like large pythons) which the cast majority of people who get them should never be allowed to touch. If there are mechanisms in place to allow competant people to own these snakes, I see no problem with restrictions on a lot of "exotic" organisms. FOr three reasons:

1) Animals are often not cared for properly. They are NOT property, they are living things with their own interests. As keepers we have an obligation to treat them well, and this SHOULD be legally enforced.

2) Many exotics are collected commercially without regard for sustainable use from their native environments. Many like turtles and snakes do not breed in sufficient numbers to withstand this collection.

3) When people get bored of these animals they get released (or unscrupulous importers decide to release them into the local park), and become invasive. Do I need to go into why this is bad?

It is one thing to say "there ought to be a law" when the interests involved are strictly personal. For example, if someone were to say "there ought to be a law" that restricts my right to conduct my personal life as I choose, or that seeks to enforce something trivial like how I paint my house or let my yard become a mini-nature preserve that is one thing. If however the interests involve extend beyond petty tastes and personal morality, such as the care and maintenance of our environment and enforcing standards of humane care of animals kept as pets; such as protecting local ecosystems from biological invasion, or preventing neglect of animals which cannot defend themselves, then by all means... There ought to be a Law, and that law needs to be enforced.

If that means there are restrictions on what species people can own without specialized permits in particular regions based on species invasiveness, so be it.
Why would it make any sense to ban Nerodia while allowing sales of really exotic snakes and lizards from other parts of the world?
Because a lot of those organisms cannot survive in CA, while nerodia can. Not only can they survive, but they will directly compete with the native garter snakes which are for the most part (sirtalis, ordinoides and elegans not withstanding) aquatic specialists which will get their ecological butts handed to them by water snakes, to say nothing of what introduced nerodia will do to native frogs which are for the most part ALL imperilled.

One of the factors with Nerodia is that they do not make great pets.
Only when not taken care of... but that describes the majority of people who keep reptiles.