Even in countries with heavy censorship, you can tell if large groups are unhappy, they might state they are happy with their mouths, but body language, and general behaviour will show otherwise.

Also, problematic countries also frequently have some dissenters, and people that managed to flee and speak against it while outside it.

Singapore don't forbid you to leave, and all people I ever talked that went to Singapore, or lived in Singapore but where outside Singapore, mostly only had praise for the country.