Constitutionality of Healthcare

Someone brought up to me that the healthcare bill (probably a law by the time this is published) is unconstitutional.  This is an interesting argument, I thought.

The bone that people pick with the bill/ law is that it requires you to buy healthcare insurance.  This mandated healthcare, people say, is the only case in which people are forced into buying something that they may or may not want.  I brought up car insurance, though a moment after saying that, I realized that one can simply choose not to drive.  One can choose to be homeless without a job, and not pay taxes.  Contrarily, one cannot choose not to live (suicide is illegal).

Personally, I think that mandated healthcare is, ignoring the constitution, the best way to cut down on insurance costs.  Unfortunately, there is this idea that people love to pull out; they say, "it is a slippery slope."  And indeed, I can see that argument.  Many of the greatest dictators (like Hitler per-say) came to power not by a sudden coup, but by a gradual usurpation of power.  (Just a note, contrary to the many satirically posted Obama with Hitler 'stache, I am in no way comparing Obama to Hitler.

So, then, is mandated healthcare OK.  Can you justify mandated healthcare with the constitution in mind, or do you need to go outside of it?  Do you even support mandated healthcare?