"The US and the rest of the West as well as Russia are ruled by a set of ethics that have grown out of Christianity..."
False, but also irrelevant. Christian ethics have grown out of culture, so even if what you claim is true, the "Christianity" part can be entirely factored out.
That is unless you believe the absurd claims of Christianity, then you aren't even qualified to have the conversation.
"...why else do we regard human sacrifice and child abandonment as unacceptable?"
Indeed! Why else? You, in fact, are NOT qualified to have the conversation.
"There's a very legitimate argument that our present problems come from the fact that there is no overarching ethical structure that everyone will accept as the basis for decisions."
Except that there is, and it is extremist Christians who threaten it.
"In that context the commitment of Islamic countries to Islam is as reasonable. "
And what a context it is!