There is no link between private sector pay and making "positive difference in this world" as you put it. How much do maids taking care of infants or old people make? How much would you be prepared to pay such a maid? So don't think too hard about this. The world is what it is. And it's not just finance people. Programmers in Google or Facebook get paid similar packages (probably even more when you account for how well the stocks have done), and really how much of a "positive difference" do they make?

I don't know about scientists, but I reckon doctors particularly specialists get a good deal in Singapore and many parts of the world. It is relatively well-paying, though perhaps not among the highest, with excellent job security. When you have job security you can lever up significantly with less worry than if you were in a job with less job security. Borrow to the hilt to buy a property in your early 30s, and by the time you pay off the loan in your 50s, you will have a very nice nest egg. Or even move up the property ladder over time, with job security on your back.

In finance, there is much less job security. I don't know about Singapore, but in NY or London, historically only about 0.20-0.25% of entry-level FO analysts make it to VP. Then maybe about 1/3 of VPs make it to Director and (even rarer) MD level. Nowadays there are more opportunities in the so-called "buy-side", but I would think that the ex-bankers who go on to become buy-side "partners" are not much more common. These are probably the same people who would have become Directors or MDs if they stayed in banking.

To tell you of a personal experience, I started a new role at a bank several years back, and the person whose cubicle was on my left was fired on my 3rd day on this new job. Another person whose cubicle was across from mind was asked to leave about 6 months later. The person on my left ultimately found a role on the buy-side after maybe a year, but I don't know about the one across from me. This bank eventually (years later) made me redundant too, and they paid me off with a year's salary. I did manage to find a higher-paying job at another bank after about 8 months (they really wanted a person with my experience and skills), but not everyone may be so lucky.

Many people who leave finance do so for good reasons. Many of them do move to other well-paid roles outside of financial services, with corporates for example, though the pay will be less than in "high finance". But there is probably better job security in the likes of Nestle than Goldman. Hours and stress are probably much lower too. That's worth money too, though the value will differ from individual to individual.