Still No Consistent Argument

One way to tell that Democrats are wrong about the constitutionality of the mandate is by the inconsistency of their argument.

Before constitutionality was being argued, they fought the idea that mandate was a tax.  Here's a clip from This Week with George Stephanapoulous. (To be fair, some Republicans were arguing that it was a tax).

Then they argued that it was a tax, and since Congress has the power to tax, Congress has the power to mandate insurance. No Democrat disputed this logic.

Liberal judges didn't agree, but offered their own defense.  Health care significantly affects interstate commerce, and since Congress has the power to regulate interstate commerce, Congress has the power to mandate insurance. No Democrat disputed this logic.

It was appealed.  Republicans countered that this was unprecedented because never before had Congress mandated citizens purchase a good (and later pointed out that it wasn't even a single good, but a long-term contract).

Then Democrats counter-countered that Health Care Insurance is different.  Now there are two arguments offered by different people.

1) Health Care is a large part of the US economy and is therefore interstate commerce. Therefore the government can regulate it.  Regulate it means it has nearly unbound power to affect the market. (If there is a bound, it hasn't been mentioned).
2) Health Care insurance is different because there is adverse selection which leads to healthy people avoiding the market and raising prices, therefore Congress has power to regulate it.

Neither of these arguments is complete, however in arguing constitutionality.  The problems:

1) Is there a minimum size of the economy a sector must makeup before it's large enough to fall under the interstate commerce description?  Anything defined broadly enough can fall into this category and therefore all activity is fair game.  Is that the case?
If something is interstate commerce, can Congress regulate it in any possible way?  Are there any constraints to what powers Congress has when regulating?  Can Congress force everyone to buy an airplane?  Broccoli?

2) Why is this difference constitutionally relevant? Where in the constitution does it say outright or even imply that if there's adverse selection, then Congress has additional powers to regulate?