Okay, now you can be afraid of not participating in Facebook, Twitter, and LinkedIn. In this brilliant article, Solis points out that if you're not establishing an online reputation, you're falling behind competitively. He also notes that you can't be everything to everybody, so you'll have to prioritize who you're trying to reach (but that's just fundamental to all marketing.) He does a good job of summarizing the implications, and I recommend you read the whole article.
Social Capital: The Currency of the Social Economy. 2010-Mar-2, by Brian Solis
By participating in relevant online communities and publishing content that promotes our expertise as it empathizes with those seeking information and direction in a way that literally speaks to them, we begin the process of building and shaping our online reputation, brand, and persona that traverses virtual, augmented, and actual realities. ... Essentially, our brand as defined by our views, opinions, thoughts, observations, and actions, becomes a social object that requires dynamic cultivation and placement.
So one way of looking at this development is that if you want to keep your market, you better keep them infomed of your thinking.