Although I don't share your fatalism about the Yalta conference, your analysis of the situation globally at the time certainly rings true, and actions taken need to be evaluated in light of those times, not the present. No one was about to risk any more American lives for the sake of the Bulgarias (or the Latvias) of the world.
Nevertheless, it is bracing to hear the American President announce to the world that the structures of a specious stability are no longer a legitimate substitute for the freedom of self-determination.
If Yalta did not happen - the Soviets would still have occupied what they occupied but there would have been no legitimacy to their holdings. I don't think it would have changed a thing in the long run but it would not have soiled "our" hands.
I repeat again because I bet most Americans don't remember or know this fact that except for Poland all the Eastern European nations that fell under Soviet occupation were allies with the Nazis.
No American was going to die to save former Nazi allied nations from the (what I am sure most Americans considered the rightful) wrath of the Soviets.