Question: But Yogananda told that the cause of our incarnations is our earthly desires...

Answer: Yes, there is such an opinion. But this is not true for the majority of people. It is earthly desires that spur us to action on all stages of development on the Earth, except the highest ones. And it is in action that we evolve! Those who do not act do not evolve. For almost all people the causes for actions are desires — desires that are quite earthly and simple.

In the higher stages of development people become capable of accepting ideas of karma yoga, that is selfless action-service.

And only on the highest stages when a person cognizes the Creator personally, he has to think about getting detached from everything that attracts him in the Creation.

So it is not correct to preach renunciation of desires to everyone. It is karma yoga that has to be preached! It can bring harm to no one!