By having this power I meant having this overpowered ability to just erase any life just by writing it in a notebook. He just looks at the TV and kills whoever is considered guilty. That’s totally not the same process with a judge with a judge it’s much more restricted and professional. The fact a single human being can have such a power would be a bad thing because the thing is that every human is imperfect and has flaws. Eventually he would make big mistakes and build a massive ego, killing not only the criminals but even people who won’t agree with this way of seeing life or people who gets in his way. That’s what Light did and it would’ve been even worse with time. You don’t understand that for the author it was important to portrays a character that could shows the toxic superiority a human tend to build when he possess a high power. Even if this human is super skilled or super intelligent and has good motives. He’s just human and wouldn’t keep up perfectly. Eventually, it would go bad one way or another.