Loss of privilege
I believe that the phenomenon that is going on here is the loss of privilege. Up until just recently, straight people have been privileged in society. Straight people have the privilege of walking around in public and displaying affection for the person they love. They can hold hands, hug, and kiss in public without fear of being ridiculed or attacked. Gay people have not had this privilege until the last couple decades. Yes, some bold gay people did display affection publicly before that, but in most cases it ended in them being physically assaulted, ridiculed, or even imprisoned.
Straight people have the privilege of marrying the person they love, complete with all kinds of benefits. Gay people did not have this privilege in the United States until 2006 when Massachusetts first legalized it, and even now only 1 in 5 states allows gay couples to marry.
What people such as those complaining about Jason Collins' coming out do not understand is that the media and society are not praising him for being gay, they're praising him for coming out as gay. It took a lot of courage for him to do this. He is the first active NBA player to come out as gay. Surely there have been many players who were gay, but he is the first one to say it. And many people say that his sexuality shouldn't be a big deal and he should just shut up and play the game. That's absolutely true. But, the sad fact is that his sexuality is a big deal. And that can be seen by all of the people who are tweeting that he should die, kill himself, or be killed simply because he's gay. He lost some fans when he came out. Many people are disgusted by it. And why? They shouldn't be. It shouldn't matter in the slightest.
Some day in the future, it won't matter. In a couple generations, no one will care whether an athlete is gay or straight. In fact, there may well come a day when we no longer even use the labels "gay" and "straight" anymore. But that day won't come until many more gay people such as Jason Collins come out of the closet and help straight people see that we're not dirty. We're not immoral. We're just biologically different. We are attracted to people of the same sex, rather than people of the opposite sex.
The sentiment conveyed in the picture above, though, is related but slightly different. Straight people are feeling attacked because it is becoming more popular to accept gay people. A gay person coming out of the closet in the 80s or even the 90s was met with much more hostility than a gay person coming out now. In fact, many gay people who come out now are met with very little hostility but instead are met with open arms and acceptance, as was Jason Collins (I'm sure he's had many death threats, and I know lots of people are saying he should kill himself, etc, but I also know he's had a lot of positive support from a lot of people). This can feel like a threat to straight people. They have always been privileged in society and now they are losing that privilege. It is becoming the case that more often than not gay people are treated as equals, rather than as second-class.
Think about the rhetoric which is often used for the anti-equality movement. We are accused of attacking traditional marriage. We are accused of attacking the institute of the family itself. The fact that all we want is to be treated equally is seen as a threat to heterosexuality and an attack on heterosexual marriage. And, indeed, we are challenging the notion of heteronormativity. We are challenging traditional gender roles. We are challenging the idea that only straight couples can feel love which binds people together for a lifetime. These are all true. But, we are not attacking straight people. We are not claiming special privilege or special rights. All we want is equality. All we want is to be treated the same as everyone else. Let us hold hands in public. Let us kiss in public. Let us confess our love for each other. Let us get married. Let us raise children together. Let us coach soccer teams. Let us be scout leaders. Let us feel like we have a place in society. That's really all we want. We want to be welcomed and accepted. We are tired of being pushed around, literally beaten in the streets, ridiculed, insulted, told that we are evil and sinful. We are tired of being treated as less than everyone else. This is how we have been treated. Just treat us like everyone else. Respect us. Befriend us. Love us. Let us have equal access to legal rights and protections.