On Arrakis the Fremen have a deep spiritual regard for the sandworms (and essentially consider them an embodiment of their view of god), but they are also collecting water and saving it, with the idea that one day they can use their water to make Arrakis a green planet again.
However, the sandworms need desert to survive and their very nature means they spread the desert area they inhabit until it covers as much of the planet as possible.
So it would seem the Fremen goal of making Arrakis green would be counter to their spiritual worship of the sandworms.
Are they aware of this and do they recognize this contradiction? Did they have plans to preserve the desert along with making part of the planet green? It seems one of their major cultural goals would be the destruction of one of the few animals they worshipped. How did they reconcile this?