What made Jesus question at Mt 21:25 a good example for Christians or was it a bad question because the Jews could not answer? What made Jesus question at Mt 21:25 a good example for Christians or was it a bad question because the Jews could not answer?

Jesus asked the question to the chief priests: 


  Mt 21:25 The baptism of John, whence was it? from heaven, or of men?..."
  
  25 And they argued with one another, “If we say, ‘From heaven,’ he will say to us, ‘Why then did you not believe him?’ 26 But if we say, ‘From men,’ we are afraid of the multitude; for all hold that John was a prophet.” 27 So they answered Jesus, “We do not know.” And he said to them, “Neither will I tell you by what authority I do these things."


Was it wrong for Jesus to ask what he knew they could not answer because of the parameters of his question?

Answers from a mainstream evangelical doctrinal perspective please.
The question was effective, because it highlighted the hypocrisy of the religious Jews in question. According to the Bible, John was sent from God, and they knew it. Their concern was how answering this question would affect their agenda.


  if we say, ‘From men,’ we are afraid of the multitude; for all hold that John was a prophet


Denying John's God-sentness would have resulted in some backlash and punishment from the general population, which could have even escalated to the point of stoning.

On the other hand, by admitting that John was sent from God, it would remove all surface of attack on the person of John, because the authority of God was with him. Since they religiously-politically opposed him, doing so would have worked against their agenda.

This left them no option but to give no answer, which some bystanders would have understood the reason for, and revealed the agenda and hypocrisy of the religious Jews in question.