Why have veterans who have once gone to war before often highly respected by the society?
Because we helped provide the blanket of security, you sleep so soundly under. many enjoy that security, but do nothing to help provide it.
Because a lot of people respect that they risked their lives for the country.
Because they risked everything so we could have something. They put their lives on the line, and perhaps even suffered physical or mental trauma so we could live in peace and comfort
I am assuming that you mean people who have only served one tour of service. If that's the case it's because they have fought and served this country, put their life at risk so this country can be safe. They earned the respect they fought for.