One point made was, "You can't get blood from a turnip"., "You can't go to jail." and "No one can repo your car or anything like that." In other words they can't make you pay.
What they are trying to distract from is the fact that the program is administered by the IRS. So its pretty easy to see how the fines, and yes its a fine in my book, will be collected. They will simply deduct the fine from any tax return.
So this will affect millions of low income wage earners taking standard deductions. Those returns average around a thousand or two. Possibly a bit more with an earned income credit.
Those are the voters Obama claims to want to help. I doubt very much that taking the one check per year that they very much depend on will go over very well. And so do they, that's why they never mention that shrunken tax check part.