Most paranoid, grandiose, relentless conspiracy theorists can’t call a meeting with a U.S. senator. Then there’s Robert F. Kennedy Jr. A profile of Kennedy in this weekend’s Washington Post Magazine shows that Sens. Barbara Mikulski and Bernie Sanders listened politely while Kennedy told them that a vaccine preservative causes autism.

It doesn’t. It just doesn’t. Every major scientific and medical organization in the country has evaluated the evidence and concluded that the preservative thimerosal is safe. The question is settled scientifically. Thimerosal, out of an abundance of caution, was removed from childhood vaccines 13 years ago, although it is used in some flu vaccines. And yet Kennedy, perhaps more than any other anti-vaccine zealot, has confused parents into worrying that vaccines, which have saved more lives than almost any other public health practice in history, could harm their children.

Mikulski and Sanders, to their credit, both politely blew Kennedy off. That’s a sign of great progress: Not that many years ago, Rep. Dan Burton held congressional hearings on the entirely made-up dangers of vaccines. I’m especially proud of Sanders, who represents Vermont, a state with one of the highest rates of vaccine denial and misinformation.

But the more people dismiss Kennedy, unfortunately, the more obsessive and slanderous he becomes. Keith Kloor describes some of Kennedy’s recent outrageous claims in the Post profile:

The more Kennedy talked on the subject, the more his rhetoric became hyperbolic. During one 2011 segment on his Air America radio show, he accused government scientists of being “involved in a massive fraud.” He said they skewed studies to demonstrate the safety of thimerosal. “I can see that this fraud is doing extraordinary damage to the brains of American children,” he said.

Last year, he gave the keynote speech at an anti-vaccine gathering in Chicago. There, he said of a scientist who is a vocal proponent of vaccines and already the object of much hate mail from anti-vaccine activists that this scientist and others like him, “should be in jail, and the key should be thrown away.”

I got a taste of Kennedy’s delusions last year. After Slate’s Bad Astronomy blogger, Phil Plait, criticized Kennedy for speaking at an anti-vaccine conference, Kennedy called me to complain, and I wrote about our very one-sided conversation. He told me scientists and government agencies are conspiring with the vaccine industry to cover up the evidence that thimerosal is “the most potent brain killer imaginable,” and journalists are dupes who are afraid to question authority. He claimed that several specific scientists had admitted to him that he was right. I called these scientists up. Here’s one representative answer, from a researcher who preferred I not use his name because he gets death threats from anti-vaccine activists: “Kennedy completely misrepresented everything I said.”

To recap: Kennedy accuses scientists of fraud, which is pretty much the worst thing you can say about a scientist. He distorts their statements. He says they should be thrown in jail. He uses his powerful name to besmirch theirs. That name, the reason he has power and fame, is inherited from a family dedicated to public service. He now uses the Kennedy name to accuse employees of government agencies charged with protecting human health—some of the best public servants this country has—of engaging in a massive conspiracy to cause brain damage in children.

In his profile of Kennedy and in blog posts about the story, Keith Kloor is remarkably generous to his subject, presenting him as dogged and genuine. (I have a lot of respect for Kloor and have published his work in Slate.) I asked Kloor what he thinks about Kennedy after spending so much time with him. “I have conflicted feelings about Robert Kennedy Jr. and this story I wrote. I’m sympathetic to him on a human level,” Kloor said. “I came to believe he genuinely believes he’s pursuing the truth. He has a moral certitude about what he’s doing … I really think he sees himself as a martyr for a cause.”

When I read the Post story, I worried that some readers would see Kennedy as a heroic underdog. Kloor disagrees that the story depicts him in that way, and I hope he’s right. “I think he comes off as an obsessive, tone-deaf crusader on an issue that nearly everyone he respects in his professional sphere thinks he should drop immediately. … The fact that he’s been willing to keep at it, even while he’s alienating close friends and associates—truly pissing them off—astounds me. That level of stubbornness and self-righteousness is fascinating in a public figure like Kennedy, and it’s one of the elements that convinced me this was a legitimate story.”

Fascinating it is, and absolutely maddening. And dangerous. Even if some senators know enough to nod politely, thank him for stopping by, and then ignore him, Kennedy still commands large and rapturous audiences. He is publishing a book about the supposed dangers of thimerosal, which will bring him another burst of publicity and potentially cause even more parents to refuse to vaccinate their children. The number of measles cases in the United States tripled last year—an entirely preventable disease whose resurgence has been made possible in part by Kennedy’s tireless efforts.

There are a lot of people who deserve your sympathy as they work tirelessly and thanklessly to improve the world. Robert F. Kennedy Jr. is not one of them.