In the sense of a minor self-inflicted injury for the reasons you give, it is certainly older [than the 1980s]. My erratic memory suggests it was a well-known tactic in the First World War, rather too well known to officers and medics even then to be easily carried off. I found a reference in a 1933 book, Death in the Woods and Other Stories by Sherwood Anderson.
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As a literal expression describing an accidental injury it is earlier still, from the middle of the nineteenth century...A search of US newspapers found 187 items between 1960 and 1965 reporting that a man had accidentally shot himself in the foot; it’s no doubt a common injury down to the present day (it’s difficult to search for, as most examples are now figurative).
I’m sure the expression shoot oneself in the foot derives from such accidents, usually the result of incompetence, and has led to our current meaning of making an embarrassing error of judgement or inadvertently making one’s own situation worse. That men did it deliberately as a way to avoid combat is only a side meaning.