One question that prosecutors in Harris County are overly fond of asking jurors is this:
If we only present one witness, but based on that witness's testimony you believe beyond a reasonable doubt that the defendant is guilty, can you convict him?
The prosecutors then gleefully challenge, for cause, all of the jurors who say "no."
It is (the courts have held) a legitimate commitment question — because in order to serve on the jury, the jurors must be able to commit to convicting if they find the accused guilty beyond a reasonable doubt — but it's only a legitimate commitment question on paper.
The problem with the question in the courtroom is that it's hard for most people to assume something that they don't think is possible.
The question requires a juror to assume that the State can prove its case to her beyond a reasonable doubt with a single witness. Many jurors can't see themselves believing a single witness beyond a reasonable doubt (there's Biblical precedent). Asking those jurors the "one-witness rule" question (there is no "one-witness rule) is unfair because it's asking them to believe something that they consider impossible.
Most people aren't trained to question authority by rejecting the premises of a prosecutor's question. If you ask a person a question that contains an invalid premise, then insist on a yes-or-no answer, you'll get a "no." It's a sneaky question, it's unfair to the jurors, and it's inelegant.
Such gamesmanship is beneath those who are obligated to see that justice is done.