daf bit: Avodah Zarah 54

The elders in Rome were asked: if your God does not tolerate idolatry, why does He not abolish it (and destroy all idols)? They replied: if all objects of idolatry were unnecessary for the world He would, but people worship the sun, moon, stars, and planets; should God destroy His world on account of fools? They replied: then God should destroy the objects that are unnecessary and keep the ones that are necessary. The elders replied: no, that would strengthen the idolators' case, as they would say "we know these are deities because they were not destroyed". (54b)

I have heard rabbis use a different argument when Jews ask about other forbidden items -- for example, if pigs and shellfish are abominations, why create them? In this case the answer I have heard is: so Jews will have the merit of keeping the mitzvah of refraining from them. Would the rabbis of the mishna here would give a different answer if a Jew, rather than a Roman, were asking? I wouldn't be surprised.