Sadly, this seems like an entirely rational response to me. Can you even imagine what life would be like after your son did something like that? You would have to go to those lengths in order to have any privacy at all. So often photographers and ghouls and journalists intrude so vicously and pervasively that normal life just isn't possible afterwards. The intrusiveness is just too traumatic even if you were not reclusive before. It can only be vastly worse if you have any mental illness or paranoia. Problems like Loughners are not likely to just show up in a family - they do tend to run in families, so his parents may have a bit of whatever his problems are, and this cannot help them.
I feel so much sympathy for the family. Same for the families of other notorious criminals. There is actually a movie about Jeffrey Dahmer's father called "raising Jeffry Dahmer". It is very moving, shows how the parents are in a terrible position - knowing your child has done horrible things, feeling some fault (cause as parents we DO often feel fault if our kids mess up bigtime or are sick), and still loving your child. it used to be on hulu but isn't anymore.