Suspending civil liberties

Why is it becoming fashionable for heads of state, even liberal ones, to want to suspend civil liberties?

Gordon Brown faces a humiliating parliamentary defeat over plans to allow police to hold terror suspects for up to 42 days without charge.

A survey of Labour MPs by The Independent has uncovered a growing insurrection. Only 34 votes are needed to defeat the detention plans and at least 38 MPs – enough to wipe out Mr Brown's Commons majority of 67 – are vowing to oppose controversial moves to extend the existing 28-day maximum detention period.

I suspect Hillary and/or Obama will want to continue down Bush's path on this if they win. But why?