The average spending per individual in the US per year is $10000 [0]. For an all inclusive insurance plan, if you have say a $5000 deductible and are spending less than $416/month per person you are contributing less to the pool than is being spent on average per individual. You're doing good, and are de-risked for potential health costs.

A healthcare plan where you get dumped the second you have a preexisting condition removes the de-risking benefit of insurance. The only benefit then left is the negotiating leverage of an insurance company able to pay $50k for a surgery that would out of pocket be $100k, lower ambulance bills, etc.

[0] http://www.pbs.org/newshour/rundown/new-peak-us-health-care-...