It is wrong absolutely and simply so. A person is, as it were, the owner of his own body, and as such he has absolute say over what gets done to it. At this point the case for a free society has already begun to be built, though one's adversary probably does not see it. It is time to call up the second intuition, again by asking a question whose answer will seem obvious. Suppose that to supply vital industries with much-needed cheap labor, the majority of us decided to enslave all, let us say, Irishmen.
Slavery can never be justified, no matter how many people voted for it.
Now the foundations of the free society are almost entirely laid. Only one more element is required. This matter can be a bit tricky, because there will be those who think that stealing is justified in the case of a poor man stealing from a rich man. Put that possibility off for a moment and ask the hearer to answer whether theft as a general practice is acceptable. Although the intuition that stealing is wrong is strong, people are often not quite sure what to say about why it is wrong.