The collection issue is not about the line on the form or the obligation to pay. It's about the fact that the IRS has no power to extract the money from you beyond the ability to withhold it from any refund you may have coming. In most other things where the IRS has the power to collect (confiscate) money, their powers are strong. Regarding the health insurance premium, their power is weak.
This is another flaw in the program design. The assumption is that the program will work because many more people will be buying health insurance (healthy and young people) who do not buy it now, thereby providing additional premium income to offset the claims made by older, unhealthy people.
But there are few teeth in the requirement to actually buy the insurance. If you do not buy it, you are subject to a fine. In many cases, the fine is les than the cost of insurance so the financial choice many will make will be to pay the fine. Others will not do even that, knowing that it is not a crime to not get the insurance and that the only way the fine can be collected is if you have a refund coming.