Yes. I know the episode you're talking about, so the story itself kind of makes everything rosy at the end when Jack reveals it was a deception anyway.
Well it's not like he had a choice. He knew the president would never sanction those kinds of methods. And if you can make it a deception and avoid killing innocents, so much the better.
But after the scene ended, I was fairly convinced that Jack would
have actually gone through it if there was no other option. I'm pretty sure that was the point the scene wanted to drive home.
Time is ticking, it's the only leverage you've got and alternative methods (negotiation, interrogation) will either take too much time or won't guarantee compliance. So, threaten his family. He's prepared to die for the cause, but he might not be prepared for his family to be harmed as a consequence. It is a scummy thing to do, but while one family might be broken by it, even killed by it, there's also the thousands of families who are guaranteed to die if that bomb isn't found and taken care of.
The problem I can see is that it may not work. He may not break, and he could sit there taped to the screen and watch his wife and kids get bullets into their brains and not blink. Hell, he's prepared to kill thousands of other people, why not his own flesh and blood? However, all this means is that death count goes up by +4 or 5, out of already thousands, should the ploy fail and the bomb go off as a result.
He may or may not respond. But there's nothing else really to be done except ask him politely, which won't get you anywhere. If it was practical, the agent in charge might consider flying his family into the city where the bomb was supposed to go off. But in the specific case of 24, they were across the Atlantic.
But seriously, what other options are available? Offer him a deal? Interrogate him as opposed to threaten his family? What if he stalls, in an attempt to control the negotiation/interrogation? What if he lies about the location, to send you on a wild goose chase? If family is correctly identified as leverage, then exploit it. It might cost you your self-respect if you directly or indirectly allow innocents to come to harm, but if it works then thousands of innocents are safe and secure.
A deal is out of the question. If the guy's willing to die, he doesn't want to deal. He just wants the bomb to go off.