I don't think most people take commitment very seriously. The divorce rate is horrible in the US. It's almost like marriage is disposable. And no, I don't think letting gay men have the option of marrying is eroding the institution of marriage. People having affairs with other people is a much bigger problem than two men hooking up or two women living together.
Recently the LDS put out an article on why women shouldn't read romance books. The article was full of rubbish and didn't really discover the true reason why couples can't work out their relationships. The author Ms. Gilles blamed romance books for creating dangerously unbalanced women. Unfortunately, Ms. Gilles has a distorted view of romance and marriage.
Women and men need romance and intimacy to make their marriage work. Reading romance books can help a woman to find new ways to be romantic with her husband. Marriage is a give and give relationship. When you give of yourself your partner gives back. Finding new ways and to give to your partner is one sure way to keep a marriage exciting.
Men have a distorted view of marriage, not because of pornography and sex in movies, but because their parents didn't teach them how to act like loving people. Men must show their sons how to be loving partners in a marriage. I know my dad wasn't a loving partner with my mom. He was a jerk who bullied her and treated her like crap. How could my brother learn how to be a great husband if he was taught to be a bully.
Looking a pictures of naked women is far less dangerous to the institution of marriage than husbands acting like jerks to their wives. When we teach our children that it's okay for men to be jerks they learn to be jerks.
The problems of marriage failure can't be solved by telling men and women to stop looking at pornography or reading sweet romances or even erotic romance. When two people agree to be nice to each other, treating each other kindly and using kind words then the issues of marriage failure will become less.
Commitment isn't about following rules like don't read this or don't look at that, but commitment in marriage is being kind to your spouse, causing no harm by your actions. It's about giving mercy and extending grace to your partner. Loving words bring people together. Maybe a few more men need to pick up a romance book or two to learn kind words and maybe a few more women need to look at naked pictures of people so they can get in the mood for sex. I think those two things will help marriages more than any restriction ever will.