A heroine sings a song from a Hymn Crystal. Sometimes these songs are played over certain story battles. The Fridge Logic moment? You can use the girl that's singing the Hymn in the same battle, which effectively means the girl is singing two songs at once.
Taken to its logical extreme when we find out Metafalss is basically one huge Song Magic from Frelia that's still going, even though the singer is in stasis. Shortly after Croix meets her for the first time, she's shown singing Hibernation.
And both are justified because the Reyvateil simply sends some kind of signal to make the Tower play the song she is imagining as long as she can keep concentrated on the feelings that form it. In other words, the Reyvateil just sings at the start of the song, and then, the Tower takes on the role of maintaining the song and its functions for as long as the Reyvateil can keep her concentration on these feelings. Plus, Frelia was created with the purpose of not just creating and maintaining the Tower, but actually creating and maintaining the land of Metafalica itself due to having the unique capability of "streaming" her songs (which consist of creating Hymns, programming their functions and instantly singing them). However, that plan was scrapped as soon as the Grathnode Inferia hit.
The anti-goddess policy was introduced by the Alfman regime. The reason for this was because Alfman found out about the agreement between the Grand Bell and the Goddess to sing hibernation since the first attempt to create Metafalica had failed and further attempts would probably fail too. Alfman didn't like the idea of having his and everyone else's consciousness being transferred into Infel Phira so the whole anti-goddess thing was set up in an attempt to weaken the Goddess's support and buy time for Alfman's own attempt at creating metafalica using Cloche.
So in the end it was all politics. Figures.
On a similar note, what made Raki opt to kill Nenensha? I mean, I get that her job is to protect the goddess, but a simple "Hey stop doing that!" would have sufficed. As it is, her actions led to the first war with the goddess, when simply slowing down and explaining things would have led to less trouble for everyone.
Because simply there was no time to talk them down. At the rate at which EXEC_METAFALICA/. was draining off Frelia's power, she would have been killed off in the time it took to convince the Maidens to stop singing. There is also the fact that Raki is programmed in a practical and goal-oriented way, which makes her take the decisions she deems the most practical.