If someone's actually going to refuse to interact with me simply because I tell them that I don't use social media sites then well, I'm probably better off and not missing out on much.
Exactly this. There are times when people are talking to you but not asking for your personal philosophy. I'm prone to this particular mode of conversation (telling people the "why" or "how" when they asked about the "what"). If it's pertinent to the conversation then share it but don't talk at people about your well reasoned views or you risk being "that guy".
That you know of. The most common negative response would most likely be an eye roll and going elsewhere/talking to someone else.