Mandatory health insurance?

[pauamma]

so it looks (from what I saw) that the final (signed into law) health bill makes health insurance mandatory. I'm curious: setting aside the "why would anyone in their right mind *not* want health insurance" justification or justification attempt, what are the reasons invoked to make it mandatory? If someone wanted to opt out for some reason (if only because it's mandatory, benefits notwithstanding), what would be their options, and would you consider that wish reasonable?

ETA: should probably get "health insurance" and or "it's for your own good" topic tags, but I can't create new tags.