It's not just about being funded, but rather maintaining economic growth and productivity.  By 2030, there will be one retiree for every person in the labour force whereas now it is 4 and it used to be 7 so unless we can increase birth rates, dramatically increase immigration rates, or people start dying younger, we need people to work longer to maintain productivity levels and economic growth otherwise we will be plagued by stagnant growth like you see in Japan today.