Its a really sad case and shows serious short comings in the social care system. However, if a parent cannot be trusted with their child, who can?
I agree that you cant really legislate for the minority of cases involving complete nutters, and personally, I wouldnt really wish to see the state granted additional power to interfere in people's lives. Current legislation is quite sufficiant to deal with cases such as baby P, if correctly applied.
As you say, its the serious shortcomings in the system that need to be addressed. The main problem is that those in authority in this case, the prime minister, various government ministers, leaders of haringay council, head of social services, the police, and the individual social workers involved are 100% CONVINCED that the service they offer is second to none (and they'll happily show you a graph top prove it). They simply do not acknowledge that there's a problem, any enquiry will in all likelihood be a whitewash, resources that should be directed at front line services will in fact end up in the pocket of the friends of some bent PM acting in a consultancy capacity to produce a report stating everythings fine, at worst some social worker type will lose their job, only to be replaced by a cheaper, more compliant, and less experienced version, and the cycle continues.
The first step to sorting any problem out is acknowledging that the problem exists, unfortunately we seam to have a government in absolute denial, wot credit crunch ?, wot knife crime ? I guess you cant blame politicians as the electorate have a tendancy to shoot the messanger when its bad news. As JTrader's sig says, its time to get a grip