Q: Why is the Justice Society of America of such fundamental importance to the DC Universe? -- @M_Morse
A: I've been doing this column for a pretty long time, and almost every week, I get a question like this one, where the question itself assumes a pretty specific premise. Sometimes, they go as far as actually answering the question before the end of the sentence, making my part in the whole thing pretty irrelevant --- like, say, "who is the dreamiest guy and why is it Batman?" --- but sometimes, it's that premise that grabs my attention more than what's actually being asked.
All of which is just a longwinded way to say that I'm not sure I can really explain why the JSA is a fundamental part of the DC Universe, because I'm not actually sure that they are.