"Certainly any health care system is excessively burdened by unhealthy people,"
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NO- it's not "excessively burdened."  A pool of policy holders does carry risk of unhealthy people-- when it's me and the pool of other policy holders.  -- but with 'Community Rating, 'mandatory coverage,' and Obamacare, it is now the ENTIRE population in the SAME pool and you and I-- that makes your policy sky-rocket because there ARE "excessive" amounts of unhealthy population-- namely, the ENTIRE population.
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"I would argue that we shouldn't "let them" retain their unhealthy lifestyles." -- I don't follow: does that mean you want to "make them" lead a healthy lifestyle?  What- MORE laws and MORE government?
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Never before have people had access to resources to learn how to lead healthy lives-- they choose this-- they either prioritize a healthy life, or they don't.  If they don't, we shouldn't have to pay for it.