And that's why it's fair to sue them. What you're describing is callous indifference to the well-being of others that has caused demonstrative harm.
I think everyone agrees on what the fast food place is thinking. The issue is that that line of reasoning is dangerous and has legal penalties.
Think of it with "hand washing" and "fecal coliform bacteria" instead. "It's too expensive to train our workers to wash their hands after pooping, and most wouldn't anyway because we don't pay them enough to care" just isn't a defense when someone gets sick as a result.