Even in Spain mother son couple can have children, can't marry though.An NRI lady even had a girl child with her son(and another on the way) She mentioned that in Spain it was legal and was seeking opinion about the repercussions if she decided to settle in India !
In US the laws are very stringent and incest is a punishable offence except two states,namely....Rhodes island and New Jersey ! Punishment differs from jury to jury.
A lady judge even decided not to punish a mother son couple ,who had a girl child together, when medical examination of the child showed no genetical disorder and the child was normal.She only ordered the couple to stay apart !
There is a misconception in the minds of general public that all children born out of incest are abnormal. Actually it depends upon the genes, if the mother (in case of mother son couple) and father(in case of father daughter couple are carrier of harmful recessive genes).The risk percentage is 12.5. But if the parent is already afflicted by the disorder,the risk is much higher at 50%..
Now a days in liberal western countries,they are doing medical check up for bad genes,before deciding to go for children.