Same sex marriage.
Throughout the the 1990's and up til now it has been very controversial. While many people support it and believe it should be legal nation wide (and world wide for that matter) there are still many whom oppose legalizing it, despite the fact that the movement to legalize it is growing, and opposition is shrinking. In fact many people who once opposed same sex marriage now support it's legalization (I happen to be one of them).
Those who still oppose same sex marriage will often give four primary reasons why they believe same sex marriage should be illegal. Those reasons are is that they believe that it's immoral, it's against nature, it's disruptive to society, and it will increase child molestation.
Of those four reasons (and many others) there is the one thing that they all have in common: not one of them is valid.
As for the first argument, that it's immoral, is more of a matter of opinion then fact.
Not all people consider it to be immoral. In fact several religions consider same sex marriage to be as perfectly moral as heterosexual marriage.
One could even argue that not legalizing same sex marriage might be a violation of the 1st Amendment, particularly the part about freedom of religion, because one could say that denying a marriage license to a couple because they are the same gender is illegal and unconstitutional because the state would be imposing one religious belief (that being only heterosexual couples can get married and that homosexuality is wrong) over the religious belief of another (that being that homosexuality is okay, and that same sex marriage is okay under that religious belief).
The second argument that opponents of same sex marriage make is that it is against nature.
That argument is total non-sense, as it has been shown through observation that many animal species have members that are homosexual (I believe the number is somewhere between 300 to 400, but it could be much higher).
There is only one species that has shown to discriminate against the homosexuals of it's species: Humans.
Not only is the nature argument invalid, one could even say that discrimination against homosexuals is against nature.
The third argument, that it's disruptive to society, is also not true. In fact many of the best countries in the world have legalized same sex marriage. The Netherlands for example legalized same sex marriage in 2001, and is currently one of the richest and most stable countries in the world.
If anything it helps improve society because it shows that society treats everyone as equal.
Plus, it hasn't affected American society either because
what most people who oppose same sex marriage do not realize is that
same sex couples have been getting married in this country for decades
now, it's just been in the last decade that some states have begun
issuing those couples marriage licenses.
The forth argument (and one that has often been described as homophobic propaganda) is that it would result in a higher amounts of child molestation.
This argument stems from the belief that most homosexuals are also pedophiles, and that married homosexual couples would molest any children that they adopt.
Besides this accusation being quite sick, it's completely and totally false.
Every legitimate study about this has shown that homosexuals have no more higher rates of pedophilia than heterosexuals. The studies that say otherwise on the other hand are not from legitimate institutions, and are for the most considered to be fraudulent and nothing more then propaganda created by religious institutions that strongly oppose homosexuality (it should be noted that the organizations that do promote this type of propaganda are listed by the Southern Poverty Law Center as hate groups).
Now while there are other arguments that are made against the legalization of same sex marriage, these are the four big ones, and as I have shown, none of them are valid (along with any other arguments not mentioned).
The fact remains is that there is no reason what so ever to keep from allowing same sex couples from having their marriages legally recognized.