The life expectancy at age 65 (which id what really matters, not the life expectancy at birth) is about 5 years longer now than in 1940. Raising the retirement age from 65 to 70 for Social Security (which, I believe is already the plan...eventually) would get us back to the number of years, per person that was originally planned.
However, the real issue (besides this being a socialist, generational redistribution of wealth) is the number of active worker for every retiree. Raising the retirement age would improve that ratio as well.
I have been paying into SS since I was 13 years old when I got my first job. I'd be fine with retiring a little later, except for one thing. Who will hire (or retain) all these 65-70 year old's? It's already proving hard enough to get a job at 55. There many industries that WILL NOT hire workers over a certain age even though it is technically illegal to age discriminate.
For the first time in my life I am finding it difficult to find a job with over 25 years of experience in IT and a bunch of great references.
A friend of mine in his 50's has been seeking work for almost two years. He's an excellent sales rep and wanted to get into the medical device sales field. They are not hiring anyone over 40 for those positions and has been told as much to his face.