What happens to those caught up in the toxic lies of conspiracy theorists? The Guardian spoke to five victims whose lives were wrecked by falsehoods. Conspiracy theories used to be seen as bizarre expressions of harmless eccentrics. Not any more. Gone are the days of outlandish theories about Roswell’s UFOs, the “hoax” moon landings or grassy knolls. Instead, today’s iterations have morphed into political weapons. Turbocharged by social media, they spread with astonishing speed, using death threats as currency. Together with their first cousins, fake news, they are challenging society’s trust in facts. At its most toxic, this contagion poses a profound threat to democracy by damaging its bedrock: a shared commitment to truth. Their growing reach and scale is astonishing. A University of Chicago study estimated in 2014 that half of the American public consistently endorses at least one conspiracy theory. When they repeated the survey last November, the proportion had risen to 61%. The startling finding was echoed by a recent study from the University of Cambridge that found 60% of Britons are wedded to a false narrative. The trend began on obscure online forums such as the alt-right playground 4chan. Soon, media entrepreneurs realized there was money to be made – most notoriously Alex Jones, whose site InfoWars feeds its millions of readers a potent diet of lurid lies (9/11 was a government hit job; the feds manipulate the weather.) Now the conspiracy theorist-in-chief sits in the White House. Donald Trump cut his political teeth on the “birther” lie that Barack Obama was born in Kenya, and went on to embrace climate change denial, rampant voter fraud, and the discredited belief that childhood vaccines may cause autism. Amid this explosive growth, one aspect has been under-appreciated: the human cost. What is the toll paid by those caught up in these falsehoods? And how are they fighting back? The Guardian talked to five people who can speak from bitter personal experience. We begin in a town we will not identify in Massachusetts where a young man, who tells his story here for the first time, was asleep in his bed. Falsely accused of being the Parkland shooter. Valentine’s Day 2018 was Marcel Fontaine’s day off. He slept late into the afternoon, having worked a double shift the day before. When he woke up, a wave of happiness washed over him – he was in a relationship, had a job he loved at a local concert venue. His life was good. By the time he roused himself, the deadliest high school shooting in US history was already over. A 19-year-old with an AR-15 semi-automatic rifle had entered the Marjory Stoneman Douglas high school in Parkland, Florida, and opened fire. Seventeen had been killed, though Fontaine, who has no cable TV or radio, was oblivious to the tragedy. Then he received a text from a friend. A photo of Fontaine was flying around the internet and he was being accused of carrying out the terrible Florida shooting. His immediate response was bewilderment. What shooting? Where? He was in Massachusetts, 1,500 miles away. It would take a four-hour flight to reach the school. He’d only visited Florida once when he was a little boy to see Mickey Mouse. Fontaine, 25, describes himself on Twitter as a “non-binary gay queer autistic commie that loves horror movies and metal!” He was diagnosed as being on the autism spectrum as a child and for years has struggled with anxiety and a debilitating stammer. At moments of heightened stress, he flaps his hands like a bird. In short, Fontaine is a vulnerable leftwing individual who would not harm a flea, which apparently makes him perfect fodder for the sadistic mockery of 4chan, the anonymous message board that hosts alt-right activists and other extremists. A few days before the Parkland shooting, a photo of Fontaine wearing a T-shirt of Marx, Lenin, Mao and other communist luminaries dressed in party hats had been grabbed from his Instagram feed and posted by an anonymous use...