The faith of an individual has no consequence for the society as a whole if this faith is kept as a private matter. There is no problem in having an even very strongly held faith if other people are not required to live or act according to it.
The same basic fact applies naturally to all ideologies. Any ideology does not endanger the democratic society as long as it only tries to influence other members of the society so that they would want to adhere to it. That’s the way democracy should work, after all.
A faith is no more a private matter if because of this ideology there is a tendency to forcefully change even the behavior of those who do not share this faith. These kinds of faiths can be criticized in the same way as any other ideology is criticized.