I personally will never understand this?.. and I don't mean to criticize, because clearly your experience is much different than mine. And I can see where someone might give an edge to someone (in certain areas) for having been in the armed forces (leadership, humility, etc..). But to say that it should be required to have been, to me, sounds just like saying that someone should need to be Christian, male, 6' tall, etc.. (as examples) to be elected into the White House.
It's way too exclusive. Not everyone has the ability to join the armed forces, but we all have the potential to change the world, or come up with ideas to run a country more productively. So I don't see the reasoning in limiting our options as candidates, just to ensure that someone has a background in the armed forces.
If YOU favor those in the armed forces, I can understand why you'd be more apt to vote that way. But if we need to enforce it as a requirement, as though voters aren't qualified, themselves, to choose what makes a strong candidate, or what values they believe in, then where is the freedom in our democratic process?
We can't just cherry pick what qualities should be required. It's our personal right to vote for qualities that represent our beliefs best, and if that's not enough to sway the majority, I don't believe that it's worth making into rule, at the expense of going against our free choice..
Personally, I think our president should have to know what it's like to go without food for a day (or two). Or what it's like to be homeless, or to live in an area without resources and opportunity. Or what it's like to grow up with a disability, where you're purposely set to the side and treated as damaged goods. What it's like to watch a family member suffer from preventable/treatable illness or addiction.. but these will never be requirements, no matter how beneficial the experience might be in understanding the full spectrum of what our fellow people go through.
So it's not to say that I disagree, that certain qualities come from being in the armed forces that really can't be gained elsewhere, but I just don't prioritize it higher than many other things, that will never be requirements.