Given the demographics of Hong Kong and the number of people who tend not adequately save for their retirement, a compulsory savings scheme is a must for all working adults (including our overpaid and pampered civil servants - no special deals).
But not the piece of $%$ that we call MPF. There needs to be an ultra low cost default option such as a target date retirement fund invested in an appropriate mix of equites and debt and the flexibility to invest in as wide a range of investments as possible and, if you wish, set up a self-managed fund. The Australian model has worked well (for the most part) and Australia is well on its way to having one of the most robust and sustainable retirement systems in the world.
And, yes, there should be a safety net for those whose savings run out and/or were unable to save for legitimate reasons.
The alternative is an unsustainably large number of people demanding money from future taxpayers + a lot of people having a needlessly impoverished retirement.