Advocates of those with Down syndrome have strongly criticized prominent atheist Richard Dawkins' suggestions that it would be immoral not to abort a child diagnosed with the condition.

"People with Down syndrome should not be treated like second-class citizens, and anyone making that argument sets back the great progress that has been made in terms of equality for all people," said David Tolleson, executive director of the Atlanta-based National Down Syndrome Congress.

Tolleson said his organization believes those with Down syndrome and those who do not have the condition are "more alike than different," and statements like those of Richard Dawkins "promote division instead of unity."

Michelle Sie Whitten of the Denver-based Global Down Syndrome Foundation said that people with Down syndrome "can and do live long, happy and productive lives."

Dawkins, a well-known atheist writer, biologist and former Oxford University professor, sparked controversy with a Twitter comment on the topic.

Addressing a woman who said she would face a "real ethical dilemma" if she were pregnant with a baby diagnosed with Down syndrome, Dawkins replied in a tweet: "Abort it and try again. It would be immoral to bring it into the world if you have the choice."

In an Aug. 21 blog post, Dawkins apologized for the "feeding frenzy" over his brief remark, saying he intended it to be read only by the woman addressed, who frequented forums on his website.

However, he stood by his claim that in his view, "the moral and sensible choice would be to abort" an unborn baby with Down syndrome.

"I personally would go further and say that, if your morality is based, as mine is, on a desire to increase the sum of happiness and reduce suffering, the decision to deliberately give birth to a Down baby, when you have the choice to abort it early in the pregnancy, might actually be immoral from the point of view of the child's own welfare."

Dawkins said that his position "simply follows logically from the ordinary pro-choice stance that most of us, I presume, espouse."

He acknowledged his opinion is "contentious," but said that the choice to give birth to a child with Down syndrome "would probably be condemning yourself as a mother (or yourselves as a couple) to a lifetime of caring for an adult with the needs of a child."

"No wonder most people choose abortion when offered the choice."

The Down syndrome organizations said in a joint Aug. 22 statement that they were "outraged and saddened" by Dawkins' comments, saying he "strongly argued for the elimination of people with the condition."

They stressed the need for accurate information about people who live with Down syndrome.

People with Down syndrome in the U.S. have an average lifespan of 60 years and have benefited from "great strides" in medical care and research, the foundations said. They are able to take advantage of educational and work opportunities.

Most U.S. families who have a member with Down syndrome are "stable, successful and happy." Siblings often report "increased levels of compassion and empathy," and one study has found a lower divorce rate among parents of a child with Down syndrome.

The Down syndrome foundations said that about 67 percent of pregnant women in the U.S. who receive a positive result for the condition on an amniocentesis test terminate their pregnancies. However, over 95 percent of pregnant women do not choose to have the test.

Dawkins' comments also elicited a response from J.D. Flynn, a Catholic writer from Lincoln, Neb., who is the adoptive father of two young children with Down syndrome. In an open letter to Dawkins, published on the First Things website Aug. 22, he voiced concern about seeing abortion of the genetically disabled as "a moral good."

Flynn said his children are "delightful," "beautiful" and "happy."

"One is a cancer survivor, twice-over," he wrote. "I found that in the hospital, as she underwent chemotherapy and we suffered through agony and exhaustion, our daughter Pia was more focused on befriending nurses and stealing stethoscopes. They suffer, my children, but in the context of irrepressible joy."

"I wonder, if you spent some time with them, whether you'd feel the same way about suffering, about happiness, about personal dignity," he continued. "I wonder, if you danced with them in the kitchen, whether you'd think abortion was in their best interest. I wonder, if you played games with them, or shared a joke with them, whether you'd find some worth in their existence."

Flynn invited Dawkins to dinner at his home, clarifying that the invitation was not intended for debate or for condemnation, but simply to meet his children.

"I want you to experience the joy of children with Down syndrome. I want your heart to be moved to joy as well."