I recommend checking out
The Spiritual Tattoo, it covers the history of body modification and the various reasons why some people go through it.
The author of that book is a cultural anthropologist and he is covering his torso with a history of religion. To him, his tattoos are very personal, and so none of them extend below his knees or past his shoulders, so they are covered by his clothes. I think those people who get body mods to actually look scary are in the minority; nowadays it seems to me to be a statement of individuality or conformity in some form or another, the reasons for getting a tattoo are varied from person to person (for me, the reasons not to get one eventually outweighed my desire to get inked).