Among the many reasons to support same sex marriages is so that all loving couples can enjoy the benefits and legal protections afforded to spouses. In the United States, a large percentage of the population gets health insurance through their employer. The reasons for this are curious and antiquated, but the result is that employers have power over their employees in terms of the health care coverage they receive. For same sex couples, that can mean another avenue for discrimination in an employer decides that they don't personally support marriage equality.
It is not unusual to work for a company with its headquarters in another state. Just because you live in a state like New Jersey that recognizes same sex marriages, doesn't mean that you might not run into problems if your employer is located somewhere else. Among the 15 states still on the wrong side of history, employers may find ways to try to deny you your rights.
The law is on the side of same sex couples in states with legal gay marriage. Company policies that deny employees the benefits they are entitled to as part of a legal marriage are not acceptable. The problem is widespread, however, as a study by the Human Rights Campaign recently found that 34 percent of Fortune 500 companies do not offer health benefits for domestic partners. Same sex marriage rights are correcting this and other imbalances by eliminating any legal distinction between one marriage and another. If you are married and the company offers benefits for spouses, the gender of your spouse should make no difference.
Source: The Atlantic, "Legally Married, but Their Boss Disagrees," by Olga Khazan, 20 February 2015