Time to criminalise heterosexuality?

You may have heard about the recent dreadful episode in New Zealand child abuse, the murder of newborn twins Cru and Chris Kahui at their family home, populated by a full assortment of family members close and distant. Only one of them had a paid job, the rest lived communally on welfare. Perhaps you have seen that classic New Zealand film "Once Were Warriors", so take that scenario and apply it as reality in this case. And then you still have to deal with sickening reports in your morning paper:

Detective Senior Sergeant John Tims gave details from a pathologist's report that indicated the twins' heads had been bashed with (or against) a blunt object. Their ribs were fractured and one had a broken thigh.

The Sensible Sentencing Trust (the local hang'em-and-flog'em-and-hang'em-again club) wants abusive parents to be spayed.
I'm just completely flummoxed by the behaviour of this family, which has been keeping a Cosa Nostra pact of muteness, stonewalling the police investigation under the excuse of the right to silence.
Don't these heterosexuals love their children? Is the twins' mother so browbeaten into submission she cannot/will not say who killed her babies? Where was the lioness in her that would fight for her kids? Has this family no pride so it can effectively cover up murder most foul by any of its members? Has the perpetrator no honour? Or was the babies' crying just too much for his hangover or P-induced paranoia? It just completely floors me.
And then you have the spectacle of local Christian fundamentalists standing tall and proud for the right of parents to beat their children in a campaign against Green MP Sue Bradford's Private Member's Bill to abolish section 59 of the Crimes Act. "Family Integrity" released a pamphlet [PDF file] (link via No Right Turn) on how to beat your kids for 10-15 minutes to drive out 'sinful manifestations'.
One shudders to think what sinfulness Chris and Cru Kahui manifested at age 29 weeks meriting them a fatal blow to the head with a blunt instrument. It would have taken the murderer less than 10 minutes.