The fear of communism was never real (at least not real for Western leaders and militaries). The fear was engineered for the populace. If the fear of communism was real why did the Allies fight with the USSR against Japan and Germany and why did the USA proceed to carve up Eastern Europe in a fashion extremely favorable to the USSR?

You're ignoring too many variables. At the start of WW2, both Germany and the USSR had made a secret agreement to invade and take over Poland. Trying to fight both countries at the same time may have put off Germany's plans to actually invade the Soviets since the agreement didn't stop there (for a time, they were receiving food and other raw materials as part of the deal).

In actuality, the USSR didn't become part of the allies until 1941, when Hitler had launched his Eastern front invasion, while already taking over Western Europe as well.

In regards to why did the U.S let Eastern Europe get carved up? It was the Soviets who were crazy enough to throw endless amounts of bodies at the German machine. The race to Berlin was basically one big propaganda stunt by two Soviet generals to claim victory over Germany, even if the logistics of doing so was heavily rushed.

I'd like to think the allies wanted to do more back then, but they were already fighting a war on multiple fronts on every continent. It's all hindsight to say they could have also finished off Communism in the 6 years they were at war with other nations. Especially when the Soviet Army saw massive increases during this same time period as well.

If the Western World truly feared communism why did it turn its back on Rhodesia while the USSR and China openly funded/trained communist armies in Africa which, were then used to seize control of Rhodesia?

I don't deny this. They were absolutely in the wrong to have let this country fall to the Communists. The only thing I say, is from the perspective of the U.S, they may have turned a blind eye to this because Rhodesia was considered a rogue territory from the U.K, so maybe the U.S didn't want to piss off their British allies back then? But again, everything is hindsight. Looking at Zimbabwe today, the U.S would have been better off ignoring their relationship with the U.K and save the Rhodesians instead.