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.
Legally the argument would be the same as if he collected Hummel figurines, which his parents despised.
Much of the argument could center around what was involved with the domestic dispute that resulted in them asking him to leave. Whether or not that dispute was over porn, after that time their destruction of his property could be seen as vindictive by the court.