How can one respond to those who believe that listening to music is normal, as long as their heart is free of malice, hatred, and animosity?

The heart being free of malice and hatred is among the righteous deeds, but it is not the entirety of religion and legal obligations. To use this as a pretext for abandoning prayer and other obligatory duties is a grave error, because the Commander of both is one, which is Allah the Almighty. Whoever does so will have a share in Allah's saying: "Then do you believe in part of the Scripture and disbelieve in part? And what is the recompense of those who do that among you except disgrace in worldly life? And on the Day of Resurrection they will be remanded to the severest of punishment. And Allah is not unaware of what you do." (Al-Baqarah: 85). Performing some acts of obedience does not suffice for the rest of them. Among these is singing accompanied by musical instruments, for it hardens the heart, turns one away from the remembrance of Allah and prayer, and invites to sins. The Prophet (peace be upon him) warned against belittling sins.