"A Kosher (or halal) eater will never eat nonkosher (or nonhalal) food , but a nonkosher eater isn’t banned from eating kosher."
Well no, but I would never, if given the choice, buy kosher or halal food. I would also not buy pope-approved or hare krishna-blessed food either. I'm perfectly happy with stores carrying those items for people who want them, as long as they are clearly labeled so that I know what I buy.