"Deontologist" and "Moral Objectivist" are not synonyms. Most deontologists are nonetheless objectivists. The reverse does not hold since, for instance, consequentiailists are not deontologists but are subjectivists.
It is sill a caricature to say deontologists conjure up Right and Wrong out of nowhere. The most famous deontologist was probably Kant, who argued elaborately for his claims.
The persistent problem in these discussions is the assumption that moral objectivism can only work like a quasi-empiricism, detecting some special domain of ethical facts. However, nobody seriously argues for it that way.
As noted by Alicorn. moral laws can apply counterfactually just as easily as natural laws.
In secret, an unemployed man with poor job prospects uses his savings to buy a large term life insurance policy, and designates a charity as the beneficiary. Two years after the policy is purchased, it will pay out in the event of suicide. The man waits the required two years, and then kills himself, much to the dismay of his surviving relatives. The charity receives the money and saves the lives of many people who would otherwise have died.
Are the actions of this man admirable or shameful?