Put another way: there wouldn't be a point in deliberation if we didn't have biases. Our justice system trusts and (weakly) attempts to enforce the gap between those biases and prejudices that would actually interfere with the court's duty.
Vulcans might not have a problem with this, but humans so obviously do that pretending otherwise is impractical.
Sure, we can't get a perfectly impartial jury. But someone with a past trauma probably won't be able to judge the case for its merits.
This appears to be binary thinking. There are nearly infinite degrees of bias. Strong emotions are one way to ensure that someone is heavily biased. That's what the jury system is trying to avoid.
So someone who has never been abused can still be biased in literally any way. But the presumption is that without having such an emotional personal experience with it means they are less likely to be heavily biased. They'll be more likely to be swayed by the testimony in court rather than their experience outside of the court room.
Are these not to be a jury of my "peers". Are not all humans biased in one way or another. If being abused creates bias, why wouldn't NOT being abused also not create bias. We don't have perfect access to information. Sometimes in order to be considered impartial, jurors are basically expected to have no familiarity with basic fundamental news stories. Are people so disconnected from reality really "peers"?
Ultimately, I guess, it's the best we can do.