Well, it's their perception that the Republican Party, especially the religious right wing of that Party, who is targeting them. I don't remember any debates on the Senate floor about proposed Constitutional amendments regarding keeping segregation, denying voting rights to any particular group, etc.
When Republican Senators take the floor to talk about the "destruction of marriage" because of pending redefinition, it sounds like hyperbole to many people. They know that straight people will always fall in love with people from the opposite sex, and men and women (especially the latter) will always want to get married. If anyone's destroyed marriage, its the people who get drive through disposable marriages in Vegas, or those who buy tickets to movies made by people who consider procreation first, marriage-maybe later, or the revolving door of the courthouse, where one side of the building marries people, while the other side dispenses no-fault divorces.
Keeping marriage "safe from gays" is not going to change any of those things, and is not going to save marriage, if it is indeed in danger of being abandoned by people in the future.
the problem with all of your posts is - you talk about everything in reference to adults, and assume that homosexuality is genetic.
of course, the availability of gay marriage isn't going to mean anything to a bona-fide heterosexual male aged 25. its children and youg teens entering puberty who will be at risk from this. because during the years they are forming their sexual identities, acceptance and advocacy of gay marriage will now be a legitimate part of the american culture. this is exactly what the gay community wants, it can only help to swell their ranks, and their political power.
it only sounds like hyperbole to people who have a short term view of the situation.