Why create a thriving community on Facebook, Twitter, or YouTube, where all the interactions, all the search engine juice, all the customer contact information and permission, and much of the goodwill, are a feature of someone else’s domain? If those platforms disappeared, so would your community.
Build versus buy is a crucial question to ask yourself about any technology platform: do the benefits of creating custom software suited directly to your needs merit the much higher cost, time investment, technical demands, and ongoing commitment to upgrades.
You can also take advantage of social widgets and increasingly powerful API development tools offered by Facebook, Twitter, LinkedIn, and other platforms to build rich social hooks right into your website.