think the construction of cpf life is to help yourself and use your money to help some other poor ppl.. if everyone can opt out.. where to find money to help those poor ppl?
Ah, no.

You have it backwards, actually. This is about individual responsibility, a set of policies to avoid the risk that you will become a burden on the rest of society, insofar as possible.
Everyone can opt out of CPF LIFE. To opt out, go get alternative longevity insurance (of minimum or better payor quality), submit a simple form to CPF, and you're done. You're then free to withdraw all your CPF funds if you wish, with interest, except for your Medisave Account. (Medisave is another societal defense against your becoming a public burden.)
You
must protect yourself -- and the rest of society -- from elder destitution, if you can afford to protect yourself. The government insists on that much. But the government doesn't insist that you protect the rest of society specifically using CPF LIFE. You can buy private longevity insurance if you prefer, or somebody else can buy it for you if you're particularly lucky. The government insists you post a bond (contribute to CPF) from your earned income, tax free, but you can get your bond back at retirement, with interest, still tax free, if you have alternative longevity insurance.
You are also free to terminate your Singaporean citizenship or Singapore Permanent Residence, as applicable, and opt-out of Singapore, including CPF. Then you can withdraw all your CPF monies, with interest, including Medisave. Or you can leave those funds on deposit as long as you wish, and they continue to earn interest.
This is all
very fair, in my view. You have choices. But you do NOT usually have the choice to transfer risk of your elder destitution onto the rest of society. The government insists that everyone (who can afford it, and who has the right to grow old in Singapore) have at least a small amount of longevity insurance, whether from CPF LIFE or from some other reasonable source, just as the government insists that every automobile owner carry liability insurance. The government insists that you not burden the rest of society, that you take care of yourself, insofar as you reasonably can. That's what this deal is all about. (It's to protect wealthy Singaporeans from political turmoil and rebellion, in truth. Of course there are some wealthy people who don't understand this, maybe because they haven't read enough history books, but a wealthy society with destitute elderly residents usually doesn't end well.)