To you or me, the idea that you're going to achieve a better-run or more just world by placing absolute power with no accountability into the hands of a select few completely defies reason, common sense, and everything we know about human nature and the corrupting influence of power, and has probably been more thoroughly refuted by history than any other idea.
Additionally, the idea that a handful of people could have the knowledge and the capability to competently micromanage the lives of hundreds of millions of people is self-evidently absurd.
But liberals are able to suspend their disbelief when it comes to the government, because they are driven by religious longing. In their religion, the government plays the role of God, and is the key to achieving utopia (ie secular heaven) through social engineering. In reality, the government is just a collection of corruptible people like you and me, but liberals deify it in their minds, and attribute to it the same traits that we attribute to God: omnipotence, omniscience, and benevolence.
So, for instance, liberals are horrified by private insurance corporations having the choice to refuse to take a loss by insuring those with preexisting conditions (even though you can go to a different insurance company, or try to raise money yourself), but they're happy as clams about the government having the ability to deny you treatment outright.
This is contradictory, but it's understandable once you realize that in their minds, government bureaucrats are automatically selfless, wise, just, and dedicated to "equality" in all that they do, just by virtue of being part of the all-knowing, all-loving government.
Leftists continually push for a more authoritarian government because their religious fervor blinds them to the fact that it's just a bunch of regular fallen humans at the helm and nothing more, and because their religious system requires government power to engineer society in order to bring about leftist heaven (aka "utopia" aka "social justice" aka "human brotherhood" aka "progress" aka "equality").
That's what makes leftism a particularly dangerous religion. For Christians, our heaven is not of this world, and we are able to separate politics and religion to a significant degree (for instance, Christ's admonition to "give unto Caesar what is Caesar's"). Our only religious imperative with regards to unbelievers is to share the Word with them.
For liberals, on their other hand, politics *is* religion, and to bring about their heaven, they believe they must use the authoritarian state to coerce and re-engineer humanity into their idea of perfection.
And since their idea of perfection is impossible to achieve and things never operate according to their plans, they are always desperate for greater and more centralized power in the belief that it will finally give them what they need.
Leftism is similar to Islam in that both require coercive political action in this world to bring the rest of humanity into line, so it's not surprising that these are the two religions with the highest body counts.