While it received most of the attention due to the SCOTUS decision, the individual mandate is not the main problem with ObamaCare. In fact, from an insurance perspective, having (almost) everyone in the pool is better. The problem is when you combine the individual mandate with a required minimum benefit that's often too expensive for the new entrants. The result is too many people opting out and paying the tax, leaving them uncovered for serious illness or injury, and keeping the rest of us on the hook to foot the bill. This clearly defeats the purpose and intention of the mandate.
I agree with Holman Jenkins' assertion in his WSJ piece "ObamaCare—Upheld and Doomed" that a reasonable tweak to make ObamaCare more successful at covering more people without bankrupting the system is to "modify the Affordable Care Act so buying any health policy authorized by the new charter, no matter how minimalist, satisfies the employer and individual mandate." Read the article and let me know if you agree.