Chucker,
I am interested to understand the reasons why you don't think manufacturers have a responsibility in this problem; however your example does help me with that.
Your example does not follow the logic I am proposing at all, it focuses on the issue of consumer responsibility when it comes to the USE of a purchased product. The question we are pondering is "who is responsible for ensuring that places like Petco cannot start or maintain a business for profit while showing disregard for their livestock."
When dealing with problems, our society tends to focus on solutions that negatively affect the least amount of people. A novel goal, but typically these solutions don't get to the root of the problem. We tend to pinch off the ugly flowers as they appear rather than ripping it out by the roots.
My proposal grabs at the root of this problem. Putting all the responsibility on the consumer only pinches a dead flower. Consider the following "formula",
Variable 1: Kent Marine supplies kalkwasser to Petco, to sell for profit.
Variable 2: Consumers choose to buy Kent KW from Petco.
Resultant: Petco profits from the sale of Kent KW which helps them stays in business.
Remove variable 1 AND 2 from this equation, and the resultant does not exist. By removing just one of the variables, you only partially impact the resultant.
The negative effects associated with my solution are that quality-oriented LFS's are affected as well as Petco. Boycotting products means not buying them at the LFS either, until the results are obtained. This is a roots and all proposal. Manufacturers would eventually have to respond and they would, but in the mean time, lots of people would be negatively affected - not just the consumer pocket book.
Back to your example with Toyota, it helps me with my point. You can't buy a Toyota from the ethically-questionable, used-car guy down the road. Toyotas are only sold thru licensed, authorized, retailers. That methodology is in part what I am saying we need.
Karen