Obamacare's (Un?)Constitutionality

The Supreme Court has started hearing the initial arguments on "Obamacare" this week - the central issue being whether or not the individual mandate (buy health insurance or pay a fee) is constitutional. If you assume pre-Obamacare health care laws are constitutional, I've never understood how you could think Obamacare is not. But this interview with one of the main legal experts opposing the mandate helped me understand that opposition a bit better. Maybe it comes down to a very fundamental difference in thinking...

A health insurance mandate already exists: Medicare. I have to pay for it. With Obamacare, the difference is that it's a private insurance company instead of the government. From the perspective of government power versus individual liberty, they are effectively the same. If anything, Obamacare is less intrusive because there are multiple choices for your insurance plan. The government also already gives tax credits for employers to buy private health insurance, and that's effectively the same as Obamacare's mandate. In both cases, someone has the option of buying insurance or paying extra taxes. This is why I always figured that if existing law is constitutional, then Obamacare must be as well.

But here's what Randy Barnett, the lawyer from the interview, said: "Just because the government does have the power to do x, doesn’t mean they have the power to do y, even if y has the same effect as x." That seems like a simple idea, and the logic is quite basic and valid, yet for some reason it really took me by surprise. In my mind, when 2 things have the same result, I consider the differences to be unimportant - a technicality or semantics. I guess I just need to remember that not everyone thinks that way. Maybe the ultimate divide of opinion on the constitutionality of the mandate can really boil down to whether you focus more on the ends or the means... (though I suspect most people just decide based on whether they like the law).

Anyway, for anyone who thinks our pre-Obamacare health care policy was constitutional but the mandate in Obamacare is not, I'm curious to hear opinions on a couple of things:

1. Instead of making you pay some extra taxes if you don't buy health insurance, what if the bill just raised taxes on everyone and then offered a tax break for those who buy insurance such that the benefit/penalty was the exact same? Would that be constitutional?

2. Would it be constitutional if there were a public option? That way, you don't have to buy something from a private company; you can choose to get it from the government just like you're already forced to do with Medicare.