During a Senate Health Committee hearing on Tuesday, Sen. Rand Paul (R-KY) criticized the idea that parents should be required to vaccinate their children and perpetuated the notion that vaccines themselves could cause harm.

The speech—which came during the opening moments of the hearing, and in the midst of two major measles outbreaks—was framed as an argument in favor of personal liberty, a posture that Paul routinely adopts. But in offering his thoughts, the Kentucky Republican furthered the argument that it is socially reasonable not to vaccinate your kids, a mindset that the scientific community says is already worsening communal health crises.

“As we contemplate forcing parents to choose this or that vaccine, I think it’s important to remember that force is not consistent with the American story, nor is force consistent with the liberty our forefathers sought when they came to America,” said Paul, reading off a paper.

“I don't think you have to have one or the other, though. I'm not here to say don’t vaccinate your kids. If this hearing is for persuasion I’m all for the persuasion. I’ve vaccinated myself and I’ve vaccinated my kids. For myself and my children I believe that the benefits of vaccines greatly outweighing the risks, but I still don’t favor giving up on liberty for a false sense of security.”

Paul didn’t just make the case that vaccines should be voluntary, however. He used his platform at the hearing to affirmatively push the perception that they are potentially problematic.

“It is wrong to say that there are no risks to vaccines,” said Paul. “Even the government admits that children are sometimes injured by vaccines.”

Virtually all medical literature shows that the benefits of vaccines dramatically outweigh the limited risks. And many of the more outlandish conspiracies (including supposed links of vaccines to autism) have been discredited. But, here too, Paul sounded a skeptical note, suggesting that the data simply wasn’t large enough to give parents a convincing case.

“Now proponents of mandatory government vaccination argue that parents who refuse to vaccinate their children risk spreading these diseases to immunocompromised community,” he declared. “There doesn't seem to be enough evidence of this happening to be recorded as a statistic.”

Paul, who is an eye doctor, has long argued that forced vaccination is wrong, even comparing the concept to martial law. But what is often left unsaid in his speeches is the scientific consensus that parents who do not vaccinate their children create risks of communicable diseases that could impact parents who have every intention of vaccinating their kids.

That social contract has already begun to break down in places over in the past several years. According to the Centers for Disease Control, recent measles outbreaks have popped up as sickened travelers arrived in the U.S. from abroad and as the number of unvaccinated people in the U.S. has grown.

A lack of vaccinations fueled a measles outbreak that has sickened 69 people in Washington and Oregon and more than 200 in New York. In 2015, an outbreak that began at Disneyland sickened 147 people. While the initial case was not found, a study in JAMA Pediatrics, a peer-reviewed medical journal published by the American Medical Association, indicated that a lack of vaccinations helped the virus spread more rapidly.

Shortly after Paul spoke, his Republican colleague, Sen. Bill Cassidy (R-LA) offered to “give some color to what Senator Paul said.”

He then proceeded to go through cases of individuals who ended up with terrible diseases simply because they didn’t think getting vaccinated was important. A physician himself, Cassidy noted that the only requirement with regards to vaccination was that a children get them before entering the public school system.

Addressing Paul without looking at him, Cassidy concluded: “If you are such a believer in liberty that you do not wish to be vaccinated then there should be a consequence and that is that you cannot infect other people.”