Where's the Dialog

I've been searching for the Social Security "dialog" and coming up empty. On the few "Left" leaning sites I visit regularly I've only seen defenses of Social Security describing how "it isn't broken" and which go deeply into economic forecasting for the future. What I haven't seen is any defense of it on principle. That is to say, explaining

• Why the government should be in the retirement business in the first place?
• What part of my social contract does retirement fall under?
• Why, if it is a "safety net",there isn't means testing?

If any of you have seen essays addressing these issues, could you drop a URL in a comment. (That's all)
Really!