As long as the activity is safe sane and consensual it is fine. It doesn't matter if the people involved are committed or not. As long as they behave responsibly it is fine.
Though the experience is emotionally satisfying if people are in a relationship, but having sex before marriage is a personal decision, if someone wants to do it, it's their choice.
First if all most people get married in their late 20s or early thirties. No ones gonna wait to have sex until their 32. Sex is natural and the biological breeding ages for people are 18-24 so waiting until your 25 or older is unnatural and goes against nature. Don't miss out. It's meant to be a lot of fun and it's not hurting anyone.
Pre-marital sex has become more and more socially acceptable over the years. It's not uncommon to find people that have long and fruitful relationships without ever getting married. Marriage is in a sense a status symbol. People that aren't particularly religious don't hold as much weight in it. It is alright, as long as it's done responsibly.
Many people having premarital sex do not do it responsibly. Marriage isn't just a symbol for a commitment.. It is a commitment. Marriage shows that the partners will stay faithful to each other. What premarital sex creates is broken families with children born out of wedlock doomed to stay in poverty, or even worse...Abortions. Married couples and well structured families ensures a safe society by having just that- a well structured family which is composed of responsible parents, and well raised kids.