Sitting is not the new smoking. Smoking kills you outright. Sitting for long periods of time without moving will do the same. But sitting in 45 minute intervals and then getting up to take a five minute break will keep you just as healthy as standing all day at work, which probably has its own negative consequences.
Some people need to sit in order to do focused, creative work. They may stand to answer email and input data. Meanwhile, the only way some people can work is on their feet.
Marketers sell fear. They sell successful role models that worked standing up, most notably Benjamin Franklin and Ernest Hemingway. Standing up is a health recommendation, not a promise for success.
Sitting won’t kill you if you get up every once in a while, preferably for exercise.