While that can be a valid response, the map from the hypothetical to reality is often not obvious at first. This can be due to plain old inferential distance problems, or it can be a deliberate 'trick'.

If you're trying to convince someone of the truth of X, and they are emotionally involved in the truth of X, it can help to get them to agree with you on the truth of Y (of which they are emotionally neutral), and then only after they're on the same page, give them the map.

For this reason, "That is true, but I don't see any relevance" is usually a better response than "but real life isn't a hypothetical!".