Any moral context aside, I suspect the judge will ask several questions. The first of these was he staying at their residence with a written agreement, and did that agreement, oral or written, specify labor instead of payment for his tenancy?
Since he was married, the assumption was that he was legally an adult, and no longer under his parent’s supervision.
That he was in possession of something which was forbidden by his parents, their legal action was to kick him out, not to destroy it. Legally it doesn’t matter what it is. So by destroying his property, whatever it is, they are open to liability for its value.
I’m sure that’s the argument the plaintiff will use. The countervailing argument is that, as an adult, he entered into an agreement to occupy the dwelling under certain restrictions, and that he failed to live up to those obligations. If the legal remedy included in that agreement was the right to destroy the offending material, then he has virtually no leg to stand on. But proving that could be difficult unless there is a written rental agreement, which I doubt.