Persons with pre existing conditions need insurance for their health also. They should be allowed to sign up. However, it is fine if there are some limitations. Perhaps there could be waiting periods for getting care for particular things or dollar limits or a set of choices that would have to be taken into account.
Few words have ruined more lives than the words "pre-existing condition," It can mean anything. Maybe you have asthma. Maybe you have cancer. Maybe your child had a heart murmur at birth. But until the Affordable Care Act became law it meant that you could not get insurance, no matter how much you were willing to pay for it.
Banning a human being from receiving medical care is barbaric and cruel. It has no place in a civilized nation and it is impossible to justify for any reason other than pure profit.