I SAT down to watch “How to Survive a Plague,” a new documentary about the history of the AIDS epidemic, expecting to cry, and cry I did: at the hollowed faces of people whittled to almost nothing by a disease with an ugly arc; at the panicked voices of demonstrators who knew that no matter how quickly research progressed, it wouldn’t be fleet enough to save people they loved; at the breadth and beauty and horror of the AIDS quilt, spread out across the National Mall, a thread of grief for every blade of grass beneath it.

I expected to be angry. Here, too, I wasn’t disappointed. The words of a physician on the front lines in the early days reminded me that “when people died in the hospital, they used to put them in black trash bags.” Many politicians mustered little more than contempt for AIDS sufferers. “There’s nothing ‘gay’ about these people, engaging in incredibly offensive and revolting conduct,” snarled Senator Jesse Helms, a Republican from North Carolina, at the time. The documentary memorializes that rant and that mind-set, and also shows Helms saying that he wishes demonstrators would “get their mentality out of their crotches.”

What I didn’t expect was how much hope I would feel. How much comfort. While the movie vividly chronicles the wages of bigotry and neglect, it even more vividly chronicles how much society can budge when the people exhorting it to are united and determined and smart and right. The fight in us eclipses the sloth and surrender, and the good really does outweigh the bad. That’s a takeaway of “How to Survive a Plague,” and that’s a takeaway of the AIDS crisis as well.

I referred to the movie, which was produced and directed by the journalist David France, as a history of the epidemic, and it is. But it teases out a specific strand and tells a particular story, focusing on the protest group Act Up, which was set into motion by Larry Kramer 25 years ago this month. He had already sounded an alarm over the rapidly spreading epidemic with his landmark play “The Normal Heart,” and in March 1987, during remarks at the lesbian and gay community center in downtown Manhattan, he bluntly told a roomful of men that if they didn’t take bold steps to make America and its government care, two-thirds of them could be dead in five years.