I think that you might want to reference the music video when discussing the social context of the song. The subject of the video is an autistic child who is seen as the target of the social order's ire and scorn. In the end, when she writes the word "Numb" into her arm, it is a statement of how individuals who are marginalized can end up feeling about their social settings. The idea of belonging is a powerful one in the song's lyrics, as well. Notice the refrain of "Caught in the undertow" and "Every step I take is another mistake to you." In both of these, there is a distinct feeling that one's sense of identity and self are being taken from an individual. The notion of belonging in a social setting is almost akin to being invisible. In this light, the concept of being "numb" is a respite from capitulating to what society would want. In the end, "belonging" in this social order is similar to a loss of one's identity and one's identity is precariously held in the balance of asserting individual voice and being a part of this social order.