Conservatism practiced in moderation looks to the past for practical lessons and examples to emulate, but when taken to excess the tyranny of the past presumes that all questions about humanity and society have long been settled and can't be improved upon, either by wiser men than we'll ever see again, or by divine revelation. Conservatism in excess distrusts innovation and experimentation, albeit in some realms more than others, and regards the future with fear so long as it fails to conform to the timeline of the prophets. In effect, it enslaves people to the past.
Progressivism practiced in moderation aspires to a steady improvement in the quality of human life, beginning as soon as possible and continuing indefinitely into the future. When taken to excess the tyranny of the future sacrifices the present to distant visions and wages war on the past. Totalitarians presume that no no one really knew anything before they came along and see nothing the past can offer except unwelcome contradiction. Since their future is a kind of perpetual becoming, always better than what came before or what exists now, the people here and now often seem less real, less meaningful, less worthy of consideration or compassion to them. In effect, they enslave people to the future.
Liberalism practiced in moderation combines critical awareness of the past's lessons, when they're still relevant, and an awareness of the future as an extension of the here-and-now. Taken to excess, liberalism becomes the tyranny of the present, spurning all appeals to past wisdom while stubbornly prioritizing the here-and-now over the future. While conservatism in excess is often skeptical toward innovation and progressivism in excess is often skeptical toward immediate human needs, liberalism in excess is skeptical toward sacrifice, doubting the worth of future goals for the people here-and-now who'll never see long-term goals realized. As the undisputed champions of the here-and-now over both past and future, liberalism in excess -- you might call it anarchy, hedonism, individualism, secular humanism -- doesn't see itself enslaving anybody, but are they right?
The first two kinds of tyrannies have been the subject of theory and critique for ages now, but the idea that liberalism in excess is a kind of tyranny, or at least a form of oppression -- though not the "liberal fascism" of sophomoric Republican rhetoric -- is less often considered, if only because most people doing the thinking and critiquing in the world are liberals. American liberalism is arguably a special kind of excess with specific historical sources that now seems incapable of addressing challenges from the many forms of 21st century extremism. Whether that means liberalism has reached its historical limit of usefulness, or whether American liberalism is uniquely handicapped, requires further consideration of the subject, which I hope to return to every so often when President Trump and his enemies aren't making so much news.