On "Rescue Me," his character doesn't hesitate to jump into blazing buildings or self-destructive situations. In real life, Dennis Leary's jumping into the ring with Amanda Peet and Jenny McCarthy in the battle about autism.
In his new book, "Why We Suck: A Feel-Good Guide to Staying Fat, Loud, Lazy and Stupid," Leary, who has two sons, lashes out against parents who think their kids are autistic.
"There is a huge boom in autism right now because inattentive mothers and competitive dads want an explanation for why their dumb-ass kids can't compete academically, so they throw money into the happy laps of shrinks ... to get back diagnoses that help explain away the deficiencies of their junior morons. I don't give an [expletive] what these crackerjack whack jobs tell you -- yer kid is NOT autistic. He's just stupid. Or lazy. Or both," he writes.
Leary's not the first celebrity to weigh in on a debate that may be best handled by the medical community, not Hollywood. In August, Amanda Peet spoke out about autism and childhood vaccination on ABC's "Good Morning America," saying the public might be better off to turn a deaf ear to celebrities when it comes to vaccines.
"It seems that the media is often giving celebrities and actors more authority on this issue than they are giving the experts," Peet said. "I know it's a paradox, but that's part of why I wanted to become a spokesperson, to say to people, 'Please don't listen to me. Don't listen to actors. Go to the experts.'"
Peet also apologized again during her appearance for comments she made in the July issue of the parenting magazine Cookie, in which she stated, "Frankly, I feel that parents who don't vaccinate their children are parasites."
"I didn't mean to show disdain, and I did and do apologize for the use of the word 'parasites,'" she said. "But I do in no way, shape or form retract my position or the meaning behind the use of the word, which is that if there are vast reductions in herd immunity, our children will be at risk."
Peet has taken her message to the Internet, sharing her story on www.vaccinateyourbaby.org. And the actress, who stars in the new movie "X-Files: I Want to Believe," last month announced her support of the group Every Child By Two (ECBT). She is scheduled to be part of a panel on Aug. 5 to encourage parents to have their children receive all recommended vaccinations by the age of 2.
Peet says her interest in vaccines began with the birth of her daughter, Frankie, on Feb. 23, 2007.
"When Frankie was born, I started to learn about vaccine safety," she told ABCNews.com in an e-mail message. "The more I learned, the more I realized how much misinformation there is about vaccines."
Amy Pisani, executive director of ECBT, says she hopes Peet's advocacy is "a 100 percent antidote" to former Playboy model Jenny McCarthy's position that the current vaccine schedule places children at a higher risk of developing autism.
Pisani says that the issue is too important to be reduced to a showdown between celebrities.
"We don't want it to be a fight between Jenny McCarthy and Amanda Peet," she says. "This is between scientists and the public."