Any Limits?

For an example of false bravado when arguing the supposedly clear constitutionality of Obamacare's individual mandate, this two paragraph post is pretty strong. Here's the key assertion:

The biggest problem for lower court judges who want to find the ACA unconstitutional is the Raich precedent, in which the Supreme Court upheld the conviction of people growing marijuana for their own medical use under a license granted by state law. Given that the relationship between the mandate and the national economy is much stronger, it's virtually impossible to square an argument that the ACA is unconstitutional with Raich (hence, the specious "activity/inactivity" distinction, which constitutes an unsuccessful attempt to pretend that the cases are different.) 

I don't find the activity/inactivity distinction specious. But, put that aside. My question for those who claim that Congress has the power to mandate that individuals buy health insurance is this: If this is constitutional, what would Congress have to do before you would agree that their actions were unconstitutional? The reason I ask is this: when I listen to people explain why Obamacare is constitutional, I get the distinct impression that these people would never find anything Congress has done to be unconstitutional. And, that does not jibe with my understanding of the Constitution. The Consitution did not make Congress' power limitless.