McCarthy is officially named a cohost. Watch Barbara Walters make the big announcement.

"Congrats ABC for hiring vaccine crank Jenny McCarthy for her 'outrageous... fresh POV,' [because] actual medical science is so stale and dull," tweeted Time magazine's television critic, James Poniewozik, who also wrote a column denouncing the decision.

A spokesperson for ABC declined to address the controversy, saying only, "We are celebrating the announcement of her joining the show. That is our focus today."

McCarthy's personal publicist did not respond to a request for comment, nor did representatives of Generation Rescue.

Her detractors, however, were less reserved.

"She's very dangerous. It's unfortunate that in our society, scientific evidence is now just taken as some other point of view," said Specter, adding that recent outbreaks of easily preventable diseases such as measles are "directly attributable" to people like McCarthy.

Amy Pisani, executive director of Every Child by Two, said she felt "deflated" by the news.

"Any time she provides her opinion, it results in people listening," she said. "I feel that we don't have any more children to spare."

While it remains to be seen whether McCarthy will use "The View" as a bully pulpit for her opinions, the new job will bring her greater visibility and influence, even if she never so much as utters the word "thimerosal" on the air.

If nothing else, say her critics, perhaps McCarthy will be forced to defend — or even recant — her beliefs on "The View."

"I would hope that her colleagues on the show, if the subject comes up, will take issue with the erroneous information," Schaffner said. "These erroneous concepts must be rebutted and they have to be rebutted immediately."

Specter, however, failed to see a silver lining: "ABC should fire her."