Sen. Rand Paul (R-KY) doubled down on his comments that vaccines should be “voluntary” in an interview on CNBC Monday.

“I have heard of many tragic cases of walking, talking normal children who wound up with profound mental disorders after vaccines,” Paul said.

CNBC host Kelly Evans asked Paul, a potential 2016 candidate, about his previous statement that vaccines “ought to be voluntary,” and he seemed confused as to why his statement was controversial.

“Well I guess being for freedom would be really unusual,” he responded. “I guess I don’t understand the point that would be controversial.”

Evans then asked Paul about the measles outbreak at Disneyland in California.

“I think vaccines are one of the greatest medical breakthroughs that we had. I’m a big fan,” he said. “But for most of our history, they have been voluntary. So I don’t think I’m arguing for anything out of the ordinary.”

Though the senator cited alleged cases in which vaccines lead to “mental disorders,” he insisted that he does support vaccinating children.

“I’m not arguing vaccines are a bad idea. I think they’re a good thing,” he said. “But I think the parent should have some input. The state doesn’t own the children. Parents own the children.”

Watch the video via CNBC: