Invasion of the Sacred means that some people believe that something has been taken away or changed from them that is very important to them. Something that they think is very special and holy. It could be a religious or cultural symbol or practice that they feel is sacred to their group of people or society.
For example, if a group of people have a special religious ceremony that they have been doing for a long time, and then another group comes and changes the ceremony, or makes fun of it, then the first group might feel like their sacred ritual has been invaded. They might feel hurt, angry, or like something very important and special to them has been taken away.
Like when someone comes into your room and takes away your favorite toy without asking. It feels like something that belongs to you has been taken away, and it feels bad. It's important to respect and value other people's sacred beliefs and practices, even if we don't understand or agree with them.