A problem: Legal notion of responsibility -- take a stance between or including companies being permitted to sell products that may be unintentionally dangerous to their users and people suing for any (mis)use of products possible that could harm them. Two extremes: Cars with unprotected fuel tanks that drag on the ground as the vehicle moves. People buying a pencil, sharpening it, and stabbing themselves with it. Less extreme: A vehicle that notes in its advertisements that it cannot go over 60mph, and if it tops 80, it severely overheats, burning passengers. There are many possible ways to draw the line in these circumstances -- one route would pay strong attention to the seller's action, giving full binding to disclaimers that the seller attaches to an item. Is this desirable? I'm not sure whether it's in the public interest to give that much control over a transaction to the seller. Of course, for a free-market fundamentalist, the answer is an immediate yes. Another approach might be to demand that the manufacturer put forth a reasonable effort to make things safe, and have a slowly rising bar as the technology improves. This is, however, blind to the question of whether the goods should be permitted to be made in the first place. If, for example, flying cars tend to explode 20% of the time they're flown, and this figure represents a good effort by the company to make things safe, is it fair to assume that they should be made? Another approach may be to look at the consequences of the failure, and to ban the more obviously less safe ones (e.g. could result in death). This has the problem that there are cases where people might not be being coerced by the market into a product or service, and instead might actually be choosing something risky (for fun, or for a potentially large pay-off).
Although the last notion shows the most promise for something that could be worked into a metric, a lot of judgement must be involved in determinations of this sort. On a larger scale, I'm becoming more convinced over time that political theory is only strong at helping us have the general, large-scale form of government be principled -- a lot of real people are needed to exercise judgement for lower levels, and a large part of that judgement is at most loosely connected to whatever general form the state takes. Long gone are the days where I thought that Libertarian theory or Rawls might spell out every detail.