The US/Allies were fine with the March 1917 revolution--the Karenski government kept shooting American/Allied bullets with American/Allied guns against the Germans on the eastern front. The Allies weren't happy with the Bolsheviks making peace with the Germans and then taking those guns and bullets and fighting other Russians with them.

Edit: In fact, the American president was more than pleased that in his request for the US to declare war that, with the "democratic" Karenski government, the war had become Democracy vs Autocratic and it was ok to enter at that point on the side of Democracy.