Appearing Wednesday on MSNBC's The Rachel Maddow Show, Republican presidential candidate Rick Santorum said that he regretted comparing gay marriage to “man on dog” relationships.

In 2003, Santorum predicted that if the high court struck down state laws criminalizing sodomy in Lawrence v. Texas, then “you have the right to anything” including pedophilia and “man on dog” relationships.

“If the Supreme Court says that you have the right to consensual sex within your home, then you have the right to bigamy, you have the right to polygamy, you have the right to incest, you have the right to adultery. You have the right to anything. Does that undermine the fabric of our society? I would argue yes, it does ... [I]t destroys the basic unit of our society because it condones behavior that's antithetical to strong healthy families. Whether it's polygamy, whether it's adultery, where it's sodomy, all of those things, are antithetical to a healthy, stable, traditional family ... In every society, the definition of marriage has not ever to my knowledge included homosexuality. That's not to pick on homosexuality. It's not, you know, man on child, man on dog, or whatever the case may be.”

Santorum called the remark “flippant” on Wednesday.

“Why did you say the word 'dog'?” Maddow asked.

“I wish I'd never said that. It was a flippant comment made to a reporter who was not being particularly professional,” Santorum said after explaining that he was quoting the Supreme Court's decision in Bowers v. Hardwick (The Advocate reported that this is not the case).

Santorum added that he stands by “the substance” of what he said.

On the day that the Supreme Court struck down gay marriage bans in all 50 states, Santorum said that the ruling proved his “man on dog” warning to be correct.

(Related: Rick Santorum: Gay marriage ruling vindicates “man on dog” warning.)

Maddow also asked the former senator whether he believes being gay is a choice.

“I don't spend a lot of time thinking about these things,” he answered.

Maddow countered by saying that Santorum's positions on gay rights had propelled him into “a nationally famous figure.”