Here's a desperately needed canon of construction

The Choose Life Canon: If a statute is ambiguous, and interpreting it one way will save many more people's lives than interpreting it the other way, interpret it so it saves more people's lives.

For an illustration, see FDA v. Brown and Williamson Tobacco Corp., 529 U.S. 120 (2000). The FDA had interpreted Congress's delegation to it of authority to regulate "drugs" and "devices" to include the authority to regulate tobacco products such as cigarettes. Consequently it established regulations aimed at reducing the likelihood that children would take up smoking. The tobacco companies sued, arguing that that there was no Congressional grant of regulatory authority to the FDA.

The arguments included many interpretive rules, and on the basis of several of these, the majority sided with the tobacco companies. On the basis of several other rules, four justices dissented. Underlying parts of Justice Breyer's dissent was an idea that looks like a more particular instance of the canon I'm proposing: "In my view, where linguistically permissible, we should interpret the FDCA in light of Congress’ overall desire to protect health."

Maybe if the majority had accepted the Choose Life Canon, hundreds of thousands of lives might have been saved.

I suppose the principle can be generalized, as follows:

If a statute is ambiguous, and interpreting it one way causes greater social benefit than interpreting it the other way, interpret it so it causes greater social benefit.

The philosophical basis for such a canon is pretty straightforward: the purpose of the law is the common good, so the courts, which uphold the law, should err on the side of the common good.

There is also a division of powers rationale: The purpose of the legislature is to promote the common good, so the court ought to suppose that the legislation is aimed at the common good.