The entire idea of insurance is that you can assess the risk of an event in a pool of people who are paying premiums.
As soon as you say that somebody gets to wait until AFTER they have an event to join the pool, you are no longer talking about something rational.
(Irrationality is the sole province of government.)
“Pre-existing conditions” is a straw-man argument any way because current law forbids insurance companies from denying coverage after one year of the condition treatment...see Health Insurance Portability and Accountability Act of 1996 (HIPAA)
http://tlc.howstuffworks.com/family/hipaa1.htm
