But isn't that "breaking of local law" just a technicality? Its not like they are actually shooting anyone, they are just passing through an airport.
There are plenty of arbitrary laws, but technicality or not, they're breaking the law. The same would be true in your scenario if their flight between 2 US states went via the UK.
It would be funny if some states required you to carry a gun at all times. Some religions for example require you to carry a blade at all times. Of course we already have contradictory laws and people are breaking rules no matter what they do.