Voir dire is one of the mechanisms the system uses to mitigate the influence of bias and prejudice. It also educates jurors about their role, the nature of the case, and the seriousness of their duty to remain impartial until all the evidence is heard.
No one gets to stack the jury with "beneficial" members. After both sides strike the jurors they think could be adverse, the result in theory is a jury of impartials.
Attorneys have all kinds of theories as to how best to conduct voir dire, mostly based on crude and superficial stereotypes - but there's zero evidence that any of them work, in the sense of picking a jury favorable to one side.
No matter what the attorneys can figure out by observing, listening, and studying the juror bios, they cannot possibly know in advance how a particular juror will react to the evidence offered in the case about to be tried, and they cannot know how one juror will influence, or be influenced by, others in the jury room. Even those who use "jury consultants" and employ "scientific" jury selection have little to show in terms of measurably better outcomes. (Lieberman & Sales, 2007; Posey & Wrightsman, 2005).