Really? So those who believe what Jesus said, that all those who believe in Him will have everlasting life, tend to create joyless dictatorships? Methinks you extrapolate too much from too little, and have presented a sweeping generalization that cannot be factually supported. You have believed a highly selective, skewed history, a history as told by Calvinism’s enemies, but not in its own native tongue. Meet them on their own terms, in their own words, and you find them a humble, God-fearing people who sincerely wished to obey God in all things. In other words, you find them Christian.
Not all, but the Calvinists have every chance they have had. Whether Calvin's Geneva, Cromwell's oppression of the English, Scottish and Irish peasantry or the hell that was the Massachusetts Bay Colony, the theme was a joyless dictatorship in which thought crimes were aggressively pursued and punished. I guarantee that for all of their denial or chest thumping no present day loud mouthed Presbyterian would willingly spend a single day under the thumb of a Calvinist regime.