A girl's religion doesn't matter after marriage since the son gets surname from father. If Muslim men are marrying Hindus/Sikhs/Christians and not letting Muslim girls marry Hindu/Sikh/Christian men and killing female babies at or before birth, then its a problem. Otherwise who will marry leftover Muslim girls if men marry Hindu/Sikh/Christian. I hope inter religious marriages are promoted, but only on equal terms and only when no religion is intentionally killing female babies to have only male children.