The question/claim: Is the notion that "a real child is a son; a daughter is a burden/deficient" and the belittling of daughters a religious attitude? Or is it jāhiliyya culture?
What does the Qur'an say? — it explicitly condemns this attitude
The Qur'an openly denounces the pre-Islamic contempt for daughters and female infanticide:
"When one of them is given news of a female (child), his face darkens and he is filled with grief." (16:58)
"He hides from people because of the bad news: shall he keep her in humiliation or bury her in the dust! Unquestionably, evil is what they decide!" (16:59)
"And when the girl buried alive is asked for what sin she was killed…" (81:8-9) — recalled as a wrong to be called to account on the Day of Judgement.
The standard the Qur'an sets
- The Qur'an presents contempt for daughters as a jāhiliyya custom and condemns it; it treats burying them alive as a murder to be questioned.
- Children are mentioned in the Qur'an as a blessing and trust with no male-female distinction; superiority lies not in sex but in God-consciousness (taqwā).
An honest limit
- This item is clear: contempt for daughters and the "a real child is a son" notion is jāhiliyya culture, which the Qur'an explicitly rejects.
- Pressure for "a male heir," and depriving daughters of education/inheritance, are remnants of the same custom, not a command of the religion.
Conclusion: belittling a daughter is not from the religion but from the jāhiliyya culture the Qur'an itself condemns. The religion counts a child a blessing, with no male-female distinction.
Source: Qur'anic verses (M. Okuyan meal). Built on the Qur'an's explicit condemnation of contempt for daughters / female infanticide; not a fiqh fatwa.