I think there is an opportunity for tit for tat, though. If a "guardian" brings in a sick animal and then declines care, I think they should be culpable under the law for withholding care; in other words, if people are reclassified as guardians, I think they should be legally obligated to provide a minimum standard of care to their guardianships.
It ought to cut both ways. We shouldn't be held to higher liability if owners won't be held to higher standards of care. But cynical LIS thinks it would only be directed at us and our liability and owners would still be allowed to provide as little care as they wanted.
I'm not so sure that holding owners legally liable for care is necessarily a good thing, either. Humans have access to resources if their child needs medical care, and they're unable to provide it. Without a support system to take care of cases where guardians can't afford treatment, you'd basically be limiting pet guardianship to those who are able to afford the minimum standard of care, regardless of the circumstance. Some people really do believe that the poor and middle class don't "deserve" to own pets unless they can pay for all expenses, even a foreign body surgery or emergency hemilaminectomy, but I disagree. And even if I did agree, how do you logistically limit pet guardianship to that subset of people who can afford pets? What kind of enforcement would you need? What would happen to pets who were denied care? Would you fine the owners? And what would happen after that? Are people going to have to pay a fine AND pay for treatment? What happens to repeat offenders? If the animals are seized, where do they go, and who then covers treatment?
And how do you work a shelter system around this legal and ethical argument that pets are entitled to a minimum standard of care? If the shelter becomes the guardian by taking them in, how do you rearrange everything for them to be in compliance? Or do you make an exception for shelters and end up with a system where a shelter can euthanize a diabetic cat because it doesn't have the resources to manage the case but a guardian who can't afford to treat their diabetic cat gets fined? Wouldn't that just encourage surrenders? If you know you're going to get hit with a fine if you can't afford treatment, why not just dump the animal or drop it off at the shelter and let them deal with it?
This discussion has reminded me of a client I've seen a few times. She has an older dog with a rectal mass who has been beating the odds and hanging in there. After the first time I saw her, the doctor I was working with told me that about a year prior, this woman hit a very rough patch in her life. She lost nearly everything and was living in her car. But she'd still try to scrape up as much money as she could to pay for an exam fee so he could be seen. The doctor and my clinic helped her out a great deal, but there were serious limits to what we could do as far as treatment went. By the time I saw her, she was living over an hour and a half away in her new apartment that she secured after climbing her way out of that hole and landing a good job. She was so thankful for our help that she still comes back. I don't think holding a person like her legally responsible for being temporarily unable to pay for care would do much good.
edit: And talk about legislation.
Imagine being called into court to establish what the minimum standard of treatment is for such-and-such because Owner Whatshisface declined this or that but Owner Whatshisface is having Dr. McFluffyPants testify that they did meet the minimum standard of care. And imagine the animal equivalent of all of the cases of parents denying medical treatment for their children based on religious grounds.
You don't think that people would be willing to spend more money if their pets were more like their children?
Like LIS said, what the law says has no bearing on the bond people have with their animals. You could give dogs legal rights equal to human beings, and you'd still get the "it's just a dog" and "she doesn't hunt so well anymore so get rid of her" people. You can't really alter people's relationships with their pets or their views on animals any more than you can their politics. Some people may be open-minded and may change, but the law has nothing to do with it. And none of that has any bearing on how much money someone has in their bank account and how willing they are to part with some of it.