While it is easy to analyze this question from a myriad of perspectives let us focus on the most recent Gallup Poll, which is one of the most popular and recognized measure of American public opinion.
The most recent Gallup was conducted on May 8th to May 11 of 2014. This particular time period surveyed a random sample of 1,028 adults. The estimated margin of error is a quantitatively-low "plus ou moin" of 4%.
As of that date, 55% of the adults interviewed declared to be in favor of gay marriage, versus a 42% against it. Three per cent of the interviewed adults were unsure.
Looking back into Gallup we will find that the percentage of people in favor of same sex marriage has actually increased steadily. The same poll conducted on May 8th -11 of the year 2006 showed a 42% in favor versus a 56% against with a 2% of "unsure" surveyed individuals.
As a second, comparative measure, we can look at Bloomberg, which is a public opinion poll conducted by Selzer and Company. From March 7th through the 10th, of this year, the company surveyed 1,001 adults. One of the questions asked was whether they rather live in a state where same sex rights were either a) easier, or b) more difficult to obtain in order to be married.
The response was that 30% wanted to live in a state where same sex marriage rights were easier to obtain for those interest, versus a 18% who said "difficult". Interestingly, there was a 50% of the sample that also responded with "Do not care" and a 2% which was unsure. Although the 50% shows overall carelessness in the matter, what does matter is that there is a majority that sees to want those rights to come easier to gay couples, than not.
We could attribute this increase in support for gay couples to a number of sources.
A) The media- With the "coming out" and public marriages of same-sex couples who are also respected celebrities, the general public has moved from shock and curiosity to desensitization. The more they see it, the less it surprises them. We could all agree that those celebrities that have "come out" and accepted their homosexuality have taken away the stigma that used to be attributed to gay men and women in the past.
B) Performing Arts- Again, the media has a lot of influence in presenting "reality" to an eager-to-be-entertained public. Today, the most influential shows on TV, this being family shows such as "Modern Family", "House of Cards", "The Borgias", and many more, include gay characters with open relationships with other members of the same sex. Adding gay married couples or gay couples who are dating to story lines helps to further desensitize any negative emotion connected to homosexuality.
C) Public policy and Social Media -Another factor that may have helped desensitize public opinion is that state governments are buying into allowing same sex marriages. The allowance of this practice sends a strong message to the rest of the country: "Our state accepts you for who you are". Contrastingly, whenever a state shows signs of disapproval, every LBGT social group will use the social media to announce it. Under such pressure, several states such as Ohio and Idaho, have had to do turn-arounds at the last minute and declare same-sex marriages valid. As you can see, the social media is quite powerfully attached to public policy: no longer can politicians make rules that others do not find out about. If you are going to be in favor or against a group, the whole world is going to find out about it. Therefore, if you want the votes, you better include all the voters.
D) Family Values- Our country may or may have not done a sudden renaissance of values. However, many TV commercials are starting to advocate for the very basics that are no longer taught in schools: gratitude, respect, character, honor, acceptance. Seems that, with War still in our backgrounds, racial and ethnic dissension since 9/11 is still quite real. Perhaps, as a society, we are beginning to choose NOT to divide any more. We are just tired of fighting. For this reason, the value of personal peace and acceptance may be growing. We are seeing media movements against bullying, and accepting those who look different, act different, weigh more, or are less attractive. Even Hollywood has turned away from the "perfect guy" looking type and favored "typical Joes" such as Jack Black (hairy and overweight) as leading men. As a society we may have finally begun to "grow up" and move away from stereotypes...slowly, but surely.
The topic has been changed over the previous years because we have moved from a conservative viewpoint to an individual view point a more libertarian person. we know that each person has a right to thier own choices. A decade ago, homosexual marriage was not as common as it is today heterosexual marriage was the most socially accepted norm, however now, homosexual marriage is being accepted by many people as well.