for all (one) cares
One does not care (if something were to happen). The phrase always precedes or follows some hypothetical situation. You can starve to death for all I care. I am not giving you any more of my leftovers.
for all I care
I don't care if (something happens). For all I care, the whole city council can go to the devil. They can all starve for all I care.
for all —
in spite of —. 1989 Independent For all their cruel, corrupt and reckless vices, the Maharajahs were worshipped as gods by tens of thousands of their subjects.