פירוש על עבודה זרה 100:2

Sheshet explains both the difficulty and the solution. The difficulty was how can we annul a sacrificial offering. If these stones are considered offerings they, unlike idols, can never be annulled. The answer is that for an offering to be prohibited it must be like something offered on the altar, and the stones are not like the offerings we put on the altar. The stones are more like an idol and therefore when the idolater treats them with a lack of sanctity, they become permitted.