A better example is, are we free to engage in commerce if the police refuse to enforce either non-payment or non-delivery?

We are indeed. One will just have to handle counterparty risk by other means, such as only dealing with people you know well, private enforcement, meeting for simultaneous performance, etc. This is readily observable in the real world everywhere that the legal system is weak, corrupt, or absent.

BTW, and this is just a nitpick, in Western countries where the legal system is reliable, the police do indeed refuse to enforce contracts, because it isn't part of their job. Instead, it is up to a wronged party to bring a civil action to the courts. The police have no role in the matter. Contract rights are not property rights.

As another has already pointed out, the enforcement carried out by the courts almost invariably consists of awarding monetary compensation, not specific performance, which happens only in certain exceptional cases. In the UK, these exceptional cases do not include personal services.

Another example, would you say companies are free to provide employee pensions if the law says that companies can cancel pensions anytime (even after retirement) and employees (or former employees) have no recourse if a company does cancel it?

You are trying to put your conclusion into the premise of an absurd hypothetical of Cloud Cuckoo Land. A pension contract that was terminable at will by the pension provider is a pension contract no-one would sign up to. A law saying that all pension arrangements are terminable at will is not going to be passed; if passed, people would find ways to structure their retirement plans that avoid whatever legal definition of "pension contract" was present in such an absurd law. Hey, suppose there was a law that when you buy something online, the supplier has no obligation to supply what you ordered? Well, go ahead and suppose it.

You are presumably trying to draw an analogy with the current state of marriage law. It would be more productive to talk about marriage law directly. Adultery is usually grounds for divorce. That looks like contract enforcement to me -- the sort of enforcement that contracts are subject to in the real world, rather than the fantasy S&M version in which the police drag the disobedient partner back in handcuffs. Time was when the guilty party would be sent away from the severed marriage without a penny (at least, if the guilty party was the woman), but that generally does not happen today. If you think the courts should regard adultery more sternly when deciding the division of the common property, go ahead and argue that, rather than claiming that no-one can be monogamous these days because the police won't "enforce" the marriage contract.