Protestantism, at the exception of high-church pre-Rowland Anglicanism, has no basis of unity with Orthodox Russia. Catholicism, on the other hand, has no basis for disunity. If that is not self-evident, I can explain.
Tell that to the average Souther Baptist who will then tell you that you Papists aren't even Christians and are praying to idolic statues of Mary.
I've defended Catholicism to protestants a lot more often then my own Orthodox faith. About the only thing they don't say is that you make your communion waifer with kid's blood.