Wait, what? Replying to a comment that is clearly about mathematics, with a comment that is clearly about mathematics, is trolling?
The OP's comment, including " ... changing the common definition of exponential by saying the exponent could be 1 or less than one" is (a) mathematical and (b) wrong and misleading. The "common definition of exponential" accommodates any valid argument to exp(x), and to claim otherwise requires a mathematical correction to avoid misleading people.
This is a very disappointing comment line. I know not everyone here is a CS major, but if you're even CS-knowledgable you should understand what an exponential process is. It is not, as many laypeople assume, something that is "very big".
That said, I was not intentionally trolling. I do think it's possible for a SS-style benefit to sustain itself provided that an exponentially growing population, whose exponent is greater than 1, is obligated to pay in.
A country with a stagnant or declining population will probably have trouble.
You may disagree, that's fine.
Nevertheless, any population whose growth (or lack of growth) is defined by the average number of children per member will behave exponentially.
That's not trolling. It's called "mathematics."