Preventing insurers from discriminating on the basis of prior illness unlinks cost and risk and will either drive insurers from the market or raise costs for everyone.
If insurers don't leave the market, that means they can get by with less overhead and profit. If they do leave, that means this is an area for a government system, which is fine.
Seems circular -- government meddling cuts profits, so company leaves, so it's an area for a government system? Shouldn't the cost comparison be to an actual free market?