If someone is childfree by choice due to medical issues, don't bring up all the people you know or have heard about who also have those medical issues that had children and everything is fine, especially not if those people happen to be celebrities. Everyone's medical issues are different, even when it's the same illness, and maybe those other people don't have the same combination of multiple issues. Also, depending on the particular disease or disorder involved, everything might not actually be "just fine", but the problem just hasn't appeared yet.
Also, please understand that when someone makes this choice, to be childfree due to medical issues, it is not a negative judgement against anyone else with said medical issues who does choose to have children. There is no need to get defensive, even if it's you personally who has some version of the medical issues who decided to have children. The issue is so personal and for each individual to decide what the best judgement call is for their particular case.
And though I've never personally met anyone who was childfree by choice due to medical issues who did somehow consider themselves morally superior to those with the same issues who have had children, there are probably some people like that out there, so I'll go ahead and say that if you do feel this way, don't tell anybody that, and try to get over it, because it's just really rude, IMHO.