There is this conspiracy theory that's being floated around by the Conservative Christian movement known as the "Homosexual Agenda". What this theory is based upon is the belief that homosexuals are actively trying to destroy what is consider traditional morals and values, and them remaking it into their own.
The reason for this conspiracy theory is probably because there is this continuing belief that homosexuality is a choice, and not something that someone is born with, as many psychologists and biologists contend. Because of this belief it is believed that homosexuals must "recruit" people into homosexuality, and that they target children for this, as they tend to be vulnerable. This has also led to the belief that homosexuals also have a higher rate of being or becoming pedophiles. This belief is not supported by any credible studies, and the only studies that do claim this are done by organizations that have a real anti-homosexual agenda, and are very biased in nature.
Because of this belief that homosexuality is a choice, in their minds, homosexuals must be actively trying to change society into something that is corrupt and perverted. It is believed that homosexuals are trying to do this through getting the government to legally recognize same-sex marriage and increasing legal protections under the law. From what I have seen, this isn't true at all. They just want society to accept them equals, rather then reject them simply because they're not sexually attracted to people of the opposite gender.
There is also this belief that homosexuals are trying to create laws that are aimed at destroying Christianity. This comes from the belief that homosexuals can not be Christians. Neither of these beliefs are true at all. In fact there are many homosexuals who are Christians, and in fact there are several homosexual, Christian preachers, who do preach in mainstream, Christian church denominations.
The biggest problems with these beliefs is that not only is there no proof that legally recognizing same-sex marriage and increasing legal protections is actually damaging to society, not doing so might actually be more damaging to a society which is changing it's attitudes towards homosexuals, not to mention the fact it's basically treating a certain group of people like second class citizens. This, and anti-homosexual propaganda spewed out by politicians, makes some homophobic people feel justified in committing acts of violence towards homosexuals, most especially homophobic teenagers, who might already live in a homophobic environment.
Homosexuals don't want to destroy society, and they don't want to destroy Christianity, they just want to be accepted and treated like equals, and not like second class citizens.