Why do people thank post-Korea U.S. veterans for protecting their country?

https://www.quora.com/Why-do-people-thank-post-Korea-U-S-veterans-for-protecting-their-country-They-lost-a-useless-war-in-Vietnam-fought-a-useless-war-in-Iraq-and-killed-civilians-The-war-in-Afghanistan-was-somewhat-justified-but-wasn%E2%80%99t-%E2%80%9Cprotecting-the-US%E2%80%9D-border