And are you joking with that second paragraph?
Not to start a huge argument over it, but here's what I think. I read some stuff on it a while back, but mostly too lazy to google it. lol.
To me, stairs are unnatural devices and not designed for the human body. Honestly, this test should have three possible paths: stairs, slopes, and escalators. I'll bet people would prefer slopes than stairs, only because stairs are totally unnatural to the human body.
No where in nature would you find a stairs. The closest thing would be a slope. When you compare a slope to stairs, there is a fundamental difference in your body's motion. On stairs, you have no control of your leg’s strides and you must walk up in an awkward angle your body wasn't meant to do a lot of.
On slopes, though, you move freely on your own strides, so the motion comes naturally and without discomfort provided you’re at about a 30~40 degree angle. Why do old people have trouble walking up stairs? And not a slope? And the answer is that stairs are totally unnatural to the body and you cannot control your motion up. Thinking about if, it you had four steps, and a small slope next to it, looking at an older individual or a person of extreme weight, you’ll notice they struggle with the steps, but not the slope. The disadvantage is that it puts a lot of pressure on your knees while walking up and over time, it would create a problem sort of like a life time runner on streets.
Honestly, if you want a good stairs exercise, go down the stairs, not up. And if you want to practice, go at a 3.5 incline on the treadmill at least 3.5 mph. You'll stimulate street level walking, and you'll put least amount of pressure on your knees.
Honestly, though, I think most people are like, "Hey, you won't hurt you knees" and stuff like that and call it baloney. But I think these people are the very same people 20, 30 years from now walking on canes. If there is a possibility that your knees could be affected, you should take a minimal precaution to minimize such activities to a tolerance point. Which is why if you're going to walk up 10, 12 floors of stairs daily, you should minimize it to about 3 times a week. But if you're walking up at home, like 13 steps, then yeah, it's nothing to worry about.