She didn't say that she wished she was never born. She said she wished her grandmother had access to the services of planned parenthood, which provide wide ranging support to poor woman, including counseling, adoption services, and comprehensive pre and post natal health exams.
Chelsea revealed that her much-admired maternal grandmother was born of an unintended pregnancy the child of unwed teenage parents who did not have access to services that are so crucial that Planned Parenthood helps provide.
Ronald Reagan's family was saved by government during the Great Depression. Specifically, his father and older brother were given government jobs at a time when they were close to losing their home. As a result , Reagan not only supported FDR, but campaigned for Truman. In his first biography "Where's The Rest of Me", he admits that his family was saved by FDR. This book has since been removed from the shelves by the Reagan Legacy Project, but don't be afraid to use your google.
Point is, by undermining the safety net that saved him, does Reagan wish he didn't exist. Or, like Chelsea Clinton, does he have a right to his political beliefs without having morons turn them into straw men?