BTW stopping people gambling it away is the reason for mandatory National Insurance, and is an argument for having higher top rates of National Insurance and other progressive, welfare-supporting taxes.
As a nation we know perfectly well that the majority of us will need state support at one point or another in our lives. Progressive rates of NI and tax taken over our lifetimes helps us spread those costs throughout our lives, as well as between people who through luck need more support and those who need less. We might even need the support earlier on, and make significant contributions later on.
As pointed out on this thread, there are many people who simply won't put that money aside unless forced to, even when they could perfectly well afford to.