Actually, Communism has minuses, too. It's like an authoritarian version of a Republic - one discontent city and ur whole economy goes to hell, and dont even get me started on the science. In scientific terms, it is much better than Fundamentalism, but if I am a Democracy during a war and the mass discontent overthrows my Senate, then I try again in Democracy, and if i find out that making entertainers would cripple my productive, economic, or scientific infrastructure, I just initiate a Revolution the same turn I tried to pull of another Democracy - I get to pick a new gov't right away. I choose Fundamentalism if I have lots of Science improvements and/or wonders, so I can have a superior economy and moderate-at-best science rate, so I can mass produce offensive (and defensive) units to add to my Army, not to mention the famous Fanatics. If I dont have that much Science stuff, but have some happy/economy wonders/improvements, AND quite a bit of military units to spare, I go Communist. That way, I'd not only have the benefit of totalitarian martial law, but also of happiness and economy improvements. ANd, I would probably be able to produce more military units w/o risking insurrections.
However, If you go Communist, you can still change gov't easily - all you have to do is begin building Police Stations, Colosseums, etc. to keep the people happy - and have at least one or two entertainers for a couple of turns. In a Fundamentalist gov't, it's very easy to go overboard with militarization (tons of Fanatics, etc.). Fundamentalism automatically cancels out the support cost for Fanatics - so you can train 50 Fanatics from one city and still have, say, 24 shields in that city, and noone will be unhappy - the lowest they'll be is content. So, if you decide that you need to catch up with the Science, and you wanna leave FUndamentalism, first say goodbye to your Fanatic Armies and ur other units - because Communist supports automatically up to only 3 units - after that u gotta pay the support cost or disband them. Democracy AND Republic - no free support. All those Fanatics and other units will kill you - not only with happiness (most of your citizens will gladly revolt to try to bring back the old order or another dictatorship) but also with shield-support cost (the cities will automatically disband them because of shield shortages, which would probably decimate half of your army and force you into signing cease-fire/peace because of a major lack of effective armies.
So, basically, Communism may be worth it, but consider Fundamentalism. Also, just give Democracy a second chance - it just might surprise you. In a game I was playing, I was Democratic America

and "World War II" broke out - a coalition of me, Republican India, and for a short while, Royal Germany vs. the Fundamentalist Alliance (Russia, England, Zululand), with Republican Egypt being left alone (Zululand attacked and occupied all Egypt except for THebes and then India finished the job by taking the nearly-defenseless city). I switched most of my cities to either Armor production, Alpine Troops, Paratroopers, aerial units, or ships. I built Airports to connect America to its overseas colonies in East Asia (Buffalo Airport), and West Europe (Richmond(in Spain)(took it from ENgland in WW1). I quickly took over most of England - Russia betrayed it, cease-fired me, and joined me in the final disection of the "dying Lady Protector", but then also turned on me just when I began to attack Germany, which had attempted to regain control of Munich, which was seized by India in WW1. When Russia turned against me, I decided that I would strike back hard. I just go Robotics and began churning out Howitzers. I took most of Russian "Old England" and then all hell broke loose when India joined my campaign , but gained no territory (they concentrated on the Zulus, who took over Thebes) though they helped me in bringning down the defenses of Russia. I seized Kiev, Smolensk, and Moscow, now only St. Petersburg was left. I attacked with an army of Paratroopers and Alpine Troops. The city was mine before my turn ended. THe Fundamentalist Russia fell to Democratic America. DEMOCRATIC! IT DOES WORK, TOO!!!