At least the scar was explained. His mother is a well-developed character. She's not the perfect anime mother archetype, permanently trusting. Instead, she legitimately parents her son, and she has her own level of assertiveness.

Ryoko should have stuck it out a little longer and studied Shinichi's mother during a "Home Visit." She genuinely seems intrigued about what their kind are, she's far more patient than any others we've seen, including Migi. Especially after her body's own mother appeared and spotted her instantly. With Shinichi's mother posing the same kind of question, Ryoko could have learned a lot more about blending in.

In the end, I guess Shinichi is right. The parasites are completely lacking in any level of compassion. They are purely logical beings. Ryoko is interested in study as opposed to a singular focus on, "the directive." I wonder if the host's body has more to do with it than the parasites believe. The most aggressive ones we've seen are all male or animals.

I wonder if another female parasite would be more patient and inquisitive rather than aggressive. Perhaps it is the host body's hormones having an impact on them. Migi is fed by Shinichi's blood, his panic affects them both and makes Migi's offensive abilities suffer. Perhaps Ryoko's host hormones are making her more patient than aggressive? She noticed the baby kicking with an unusual awe instead of her usual cold logic. I wonder how much she will be affected as her pregnancy progresses.