Is something like that prejudicial enough that the juror should be dismissed by the judge? Because it feels like that juror is just a sympathetic peer; do we dismiss people who are sympathetic? I think judges can dismiss jurors in death penalty cases if a juror is against the death penalty. Is that actually true, because if it is, that seems like a miscarriage of justice. So if an entire town hates the death penalty and would not convict, we just keep looking for jurors who will convict? Will they literally just find the last nine people in the state who are not opposed to the death penalty?
Juries are governed by the Jury Act 1977
Part 7A deals with the discharge of jurors.
s53A makes it mandatory for a judge to discharge a juror who:
- was mistakenly or irregularly empanelled,
- has become excluded from jury service,
- has engaged in misconduct in relation to the trial or coronial inquest.
s53B gives the judge or coroner discretion to discharge a juror who:
- has become ill, infirm or incapacitated,
- may not be able to give impartial consideration because of their familiarity with the witnesses, parties, or legal representatives, or creates an apprehension of bias or a conflict of interest,
- refuses to take part in deliberations,
- for any other reason appears to be unable to act as a juror.
Note that we are not talking about challenges by the parties themselves but only by dismissals from the bench.
Beliefs held by a juror about video games, or the death penalty, or any other thing are not, of themselves, grounds for dismissing a juror. Jurors do, and are expected to, hold a wide variety of beliefs. They are also expected to, and mostly do, put those beliefs aside and vote on the evidence impartially and without bias.
Only when "it appears to the court or coroner (from the juror’s own statements or from evidence before the court or coroner) that the juror may not be able to give impartial consideration to the case because of the juror’s familiarity with the witnesses, parties or legal representatives in the trial or coronial inquest, any reasonable apprehension of bias or conflict of interest on the part of the juror or any similar reason" [s53B(b)] or "it appears to the court or coroner that, for any other reason affecting the juror’s ability to perform the functions of a juror, the juror should not continue to act as a juror" [s53B(d)] should the judge consider discharging them.
The right to an impartial jury requires that both sides be given fair hearing by the jury and that the jury weigh all evidence before them when determining the verdict and the jurors should not use any preconceived notions. While an opinion in and of itself is not a grounds for dismissal, it can become grounds if the case touches on that aspect of a political opinion. In the case you are describing, it is likely that the 17 year old defendant was playing a video game prior to committing the crime. Whether or not you believe video games, you may be liable to aquitt because of a preconcieved biased against the game, when the game being played in question had no tangential relationship to the crime that was committed (I.E. If the defendant was playing Mario Cart and then went out and robbed a convivence store, which is a crime which has little relationship to any Mario Cart mechanics. The prosecutor may seek dismissal because, despite the game having no narrative similarities to the crime other than it was part of the timeline of the event, a belief that ALL video games increase violence is going to introduce a bias that shouldn't be there. "Mario Cart made me do it" is not a valid excuse for Armed Robbery.) But the reverse situation could happen. Suppose the defendant will be using his play time of Grand Theft Auto online as his alibi for why he couldn't possibly have committed an armed robbery at the time in question? Allowing someone on the jury who believes video games leads to violence would risk a juror who turns a blind eye to the fact that there are records of his activity in GTA that could prove he didn't do because GTA is a game that glorifies violent criminal behavior and would be biased against the defendant, who has never committed an actual crime in his life.
With respect to your question on the death penalty, it is true that those people who have a moral objection to the death penalty are excused because the fear is that justice will not be served because a juror will hold out to get the defendant acquitted and deny the use of the punishment because it is a possible outcome of a guilty verdict. They also keep an eye out for potential jurors who are in favor of expanding the death penalty as well, as they might be too eager to convict.
Ignoring evidence of guilt because you disagree with the level of punishment the defendant is facing is just as bad as ignoring evidence of innocence because of any other preconceived opinion you have on the situation. What Justice is done by the release of a person who all evidence says is guilty of horrible crimes... because one person believed the potential punishment was too harsh.
Incidentally, Capital punishment cases are unique in the U.S. Legal system in that the Jury actually has some weight in the sentancing. Unlike non-capitol offenses, where the judge is the sole arbiter of sentancing those found guilty, it often falls to the jury to decide if first if the defendant is guilty of a crime for which the Death Penalty is authorized, and then if that person's crimes rise to death penalty levels. In U.S. Law, it is unconstitutional for any crime to have a mandatory death penalty. Those that do usually have a list of aggravating circumstances that will allow for the death penalty to be used. For these cases, the jury must first determine if the accused is guilty of a crime that could carry a capitol offense, then must determine if the aggravating factors in that crime warrant the use of the death penalty (was the prosecution able to prove beyond a shadow of a doubt that the aggravating circumstances occurred.) and make a recommendation to the judge of capital punishment based on that... the judge has the ultimate determination during the sentencing phase of the trial, by which point the jury is dismissed.