Sure, this would cause unnecessary stress on the lower back as well as other joints. You aren't going to be able to have correct posture for things like typing at a computer for an extended period of time while standing up. The people here who work away from a desk, at a bench top, are limited to 15 minutes of computer use at a time while at a standing terminal. There is a thick floor mat and adjustable keyboard and mouse trays to get the proper posture. Even with all this, you are going to do damage over extended periods of time. Standing would be fine if you could maintain proper posture but it not going to work for all employees.
It's simple, standing desks require too much training and rely too much on the user to use properly. Companies are able to have less liability by sticking to the traditional sitting desks. Not saying you can't do it with standing, but few companies are going to take on the risks.
Good points. I would have to agree with you that a weak correlation that may or may not be causal such as the heart health of sitting down for extended periods of time has a lot less liability attached to it than a standing desk and the pain associated with improper posture.
The workplace wouldn't be forcing employees to sit up or stand down to work though, it's simply having the option to do either. There are also mechanized desks that raise and lower so you can alternate between positions. Which would be the best option as you can easily switch to reduce fatigue.