Online dating sites put you in contact with other people who are looking for a partner. This gives you the opportunity to meet the person you are looking for in a more efficient manner than going out to a bar and trying your luck. They put you in a place to succeed.
I met my wife on a dating website. Although skeptical at first, we got to know each other and are currently still together 5 years later. We have a beautiful daughter together and plan to have another one in the near future. Dating sites are ways to meet people who would otherwise not be reachable due to opposite interests in everyday life.