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This is a RUSH transcript from "The O'Reilly Factor," April 11, 2013. This copy may not be in its final form and may be updated.

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O'REILLY: "Personal Story Segment" tonight. More evidence that gay marriage now being used to punish people who don't agree with it. Our pal Rick Santorum was invited to speak this month at the Grosse Pointe South High School outside of Detroit, Michigan. But the superintendent of schools for that district Dr. Thomas Hardwood cancelled Santorum's appearance saying that he's a bigot because he opposes gay marriage.

Now the educator didn't use the word "bigot". He used the word "extreme". But we all know what the code is, do we not?

And joining us now from Washington is Rick Santorum. So, a funny thing happened when we called the school district in Michigan. A magical - - about two hours later, a magic piece in the paper appeared.

It said now that you can go. But in order for the students to hear you speak, they have to get a permission slip signed by their parents. And you say.

RICK SANTORUM, FORMER PRESIDENTIAL CANDIDATE (R-PA): I say that's disappointing that, you know, someone who served two years in the -- two terms in the senate, two terms in the house, ran for president and, by all admissions, came in second place in the republican primary, almost won the state of Michigan and actually tied in the number of delegates, campaigned extensively in that state, that to have someone like that come and speak at your school, that you would need a permission slip from your parents.

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As if there is something that that person could do to harm your child.

O'REILLY: No, I know. But isn't it logical, based upon what's happening now in the gay marriage debate, because the gay marriage people, --

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-- the pro-gay marriage people, have defined it as a civil rights issue. And they've been successful in doing that. The media has adopted that.

It's marriage quality. Whenever you see the word "equality," you know what they're going for. It's the rights issue.

And you are seen as an opponent of gay marriage, which you are. So, therefore, if you oppose, senator, equality, you're a bigot. And we can't have bigots talking to the kids.

You know what, you know what the campaign is. And it has been very successful, has it not.

SANTORUM: It has. It's been very effective. And the fact of the matter is, that's a grave concern that I think a lot of folks have, hopefully, on both sides of this issue.

That there are some, on the other side of this issue, who have chosen that if you oppose changing the definition of marriage, then you do so out of animus.

You don't do it because you have strong convictions. You believe marriage is a good thing or that holding on to that natural marriage is a positive thing for society. You do it only because you hate people who are gay. And that's wrong.

O'REILLY: Yes. The negative always overrides the positive in the debate. Now, why do you -- what's your number one reason for opposing gay marriage.

SANTORUM: Well, the number one reason is because marriage is the union of a man and a woman for the purpose of coming together to build a building block for society and having children.

Marriage is -- lots of aspects of marriage, you know, romantic love is an aspect of marriage. But it's more than that.

Every civilization in the history of man has guarded marriage and celebrated marriage because it is the one thing that helps society continue. And if marriages go away, then you don't have stable families raising the next generation.

And if you look at places that, in fact, have gone through and changed their definition of marriage, what you have seen is lower birth rates. What you have seen is lower marriage rates. What you have seen is problems that come from that.

So, the biggest issue is we need to encourage men and women to come together and form stable families and have children so society can continue. Because if that doesn't happen, it won't.

O'REILLY: All right. Now, let me play devil's advocate here. What about the argument that two homosexual individuals, be they men or women, can adopt a child who's in the foster system, who nobody else wants to adopt, and raise that child in a loving home as a good American citizen.

And they would like that child to know that their union is accepted in a legal sense by their country. What about that argument.

SANTORUM: Well, I would say that, you know, we allow adoption for single people and we --

O'REILLY: And gays, gays can adopt.

SANTORUM: In some states, they can. And so, you know, that's really not an issue. I mean, a single mom who is raising a child or is raising an adopted child -- I don't, I hope, we don't look down and say, well, you know, that she's not capable of doing that or shouldn't be able to do that because she is not married.

I don't think we say that at all. We think we want to provide stable homes for children.

But marriage is something very different. And we need to encourage men and women to come together and form those unions to provide the best opportunity to, obviously, have children and raise children.

O'REILLY: But would we be discouraging heterosexual marriage by allowing gay marriage.

SANTORUM: Yes, I believe we would. Because we'd be saying marriage isn't about children, isn't about having children, isn't about raising children.

And when we say that, then of course, you know, the consequences are you're going to probably have less children. It's happening, as we, it's already happening in America.

Before this whole gay marriage debate, we really have seen a change in what marriage is in America. So, this is sort of a logical extension.

I admit that. And, you know, there are those on the other side who say, "Well, you know, marriage is already, you know, been destroyed."

And in many respects, they are absolutely right in that it's -- the centrality of marriage is about this union of a man and a woman having children and furthering society has been diminished.

O'REILLY: No doubt about it. The statistics show 41 percent now, as we said last night, of American babies born out of the marital realm, where in the 50s, five percent.

SANTORUM: Yes. And I think most people, on either side of the issue, most people say, "That's probably not a good thing for our country." And we don't need to encourage more of that. That's my concern.

O'REILLY: Senator, it's nice to have you back on the program.

SANTORUM: Thank you.

O'REILLY: We appreciate you're going to be able to speak to the kids in Michigan. We're glad we could help make that happen.

SANTORUM: You did. Thank you, sir.

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