When age 65 was decided upon, life expectancy was about 50. Now life expectancy is around 80.
You can not expect a fund survive when the 'takers' outnumber the 'givers'.
If you can see that don't you think accuaries can see the same problem? Back when SS started there certainly were a lot of people who collect a lot more then they ever put in. But that is natural when something starts new. That time has passed those who are lining up for SS paid their entire lives. They were promised a payment in return, now is their time.
I went through the numbers before. Yes, the life expectancy at birth when SS started was lower then it is today. But the life expectancy at 65 is approximately the same. In colonial times if a woman could make it through her child bearing years she could expect a long life, not much different then today.
Never the less actuaries look at these numbers, they recognize a problem, IN THE FUTURE, and steps will be taken.