There is also the possibility of unknowingly having children with a half-brother or half-sister.

Which was the issue in those songs I linked to earlier at 02 Dec 06 - 04:49 PM.

Clearly there are situations where checking out the biological facts are justifiable. But I don't think repudiating parental responsibility late in the day, once it has been accepted, is one of them. Even if it was based on a misconception.