I currently subscribe to the argument that says making people guardians instead of owners will open the door to larger lawsuits against veterinarians akin to what is seen in the MD world, which will drive our liability insurance through the roof, which will increase the overall cost of care, which will decrease the care given to the average animal.
So I view it as a bad thing from a medical point of view. I don't have a strong enough background in ethics to have much of a useful opinion from that perspective.
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.