The people of Boulder should assume that they live with mountain lions and bears, regardless of whether they can see them or not, and act accordingly.
Right after I moved to Colorado, I took my cat to the vet, and he inquired as to whether the kitty was an outdoor cat or an indoor cat. "Indoor", I said.
He told me that that was good, since, living near a large park (I was living in the middle of a city, mind you), he sees instances of mountain lions, coyotes and bears taking cats and small dogs from that area of the city frequently. He told me to watch the "lost" signs in the early spring and fall, and I'd see what he meant.
Sure enough, every spring and fall, you'll see more lost pet signs than you can shake a stick at, especially in areas near the foothills and near parks.
Leave your pet outside, allow your pet to roam near wooded areas or in the foothills, feed your pet outside, or fail to secure your trash cans, and you almost certainly will eventually have a problem.
It isn't the lion's fault for being a lion.
Early one morning driving in Seattle I saw a coyote scoot across the 4-lane road with a large black and white cat in its mouth. I had to laugh (sorry cat owners, of which I am one) on how that cat probably thought it was the biggest, meanest hunter around preying on the mice and birds in the neighborhood, until.....
There is no doubt that the lion was just being the lion. There is no “blame” involved.
But the reality is that this lion has lost his natural fear of humans. He is now a danger to humans. Not the lion’s fault. Not mankind’s fault. These things happen, again, no “blame” involved.
But reality being what it is, the odds are greatly increased that this lion will eventually attack a human, whether it is a child, an elderly person, or a smaller female.
It still won’t be the lion’s “fault”, because the lion is just being a lion.
But human’s being human, we can see this possibility and we value a human life more than a mountain lion’s life. That is why the cat must be put down. He is now a danger to some human.