Dr Stocker answers my concerns about free-riding and rent seeking with this gem:

Good points Brandon. On the rent seeking, I think you are broadly correct, but I would offer two qualifications. European nations/the EU often foot a lot of the bill/take on associated civilian tasks where America has taken military action, so that the US is not subsidising the defence and security needs of Europe quite as much as it might seem. So for example, in the Yugoslav breakup led to US military operations and a comparatively passive role for Europe, but a lot of the afterwork was taken on by Europe and there is no point in military intervention without work on building civil society to create long term security and stability. Going back a bit further to the first Gulf War/expulsion of Saddam from Kuwait, Germany and Japan did pay a lot towards the cost in return for not participating. Despite [this] they got a lot of abuse in the US Congress from politicians who don’t appear to understand that their non-intervention in the Gulf owed a lot to constitutions and attitudes which the US encouraged/imposed during post-World War II occupation. Recently, though European govts have been cautious in what they say in public about the Ukraine crisis and containing Putin, there is a growth in military spending and co-operation done in fairly quiet ways largely with the aim of deterring Putin from adventurism in the Baltic states. Just one example, Germany has recently taken 100 Leopard II tanks out of retirement and work is underway for the Leopard III. Moving to the Pacific, Japan is enhancing its military and weakening constitutional restrictions on the deployment of the military (imposed by the US in the post-war Constitution) in reaction to Chinese assertiveness.

While I think it is broadly correct that the US has been paying for a military burden which should be born by Europe and Japan, the situation is not as extreme as it often assumed in the US and as far as I can see is moving in a more balanced direction. In general while it is true that the US has a very impressive military machine with some impressive technology and officers, I think some Americans are a bit over confident about this. A lot of Americans, at least amongst those who take an interest in military kit, appear very convinced that the Abrams 2 is the best tank anywhere, I would suggest that in military capacity, for cost, the Leopard II is probably better (it certainly does much better in export markets) and even in absolute terms ignoring cost, the French Leclerc (which is extremely expensive) has a good claim to be the best tank around, and the Korean K2 is another strong but very expensive candidate. The Abrams is expensive, heavy, difficult to transport and difficult to keep in sufficient fuel, though it can certainly do a very good job. A lot of Americans appear to be incapable of thinking of France as anything other than a surrender monkey joke in military terms, which is really very far from the reality, as can be seen by the very strong role that France is now taking in northwest Africa against violent Islamist fundamentalists. The US military may well be able to have the same military capacity for lower cost if it moves away from the Abrams II model of a tank that is expensive to run and transport as well as build.

So broadly a correct point Brandon, but I think the situation is a bit better than is often understood in America and is moving in the right direction as Japan and Europe are getting used to the idea of taking responsibility for dealing with new threats from China, Putinist Russia and the hydra of Islamist fundamentalists.