Seconded!
That, too!
Walking is good for you. Wearing down, ptooie.
Humans are actually unusually good at long distance walking, within the animal world. In fact, in warm weather, a human can outwalk a horse. We evolved by chasing big hoofed animals until they dropped from exhaustion. Jeez, look at us, half of us is just our damn hind legs. We are so good at walking, walking, walking that we have a completely bizarre design as a result. Walking is definitely a human athletic specialty.
living will also wear you out. if you do it long enough you’ll eventually die because of it.
As one with Osteoarthritis, let me say: the body certainly does NOT regenerate all tissues.
Cartilage and nerves come to mind.
And, with renal failure, I get to see the limits on the production of red blood cells. Until very, very recently (Genentech, which created the miracle drugs, was founded in 1976) renal failure meant advanced anemia. The drugs involved were famously abused by Lance Armstrong (never take US Govt money and then commit fraud - they will come after you).
By “hiking”, do you mean that you are simply walking on relatively level ground in a forest, or are you walking up and down mountains?
I will tell of my own experiences with these activities. See also the nearby thread Does a StairMaster actually simulate climbing stairs? in which I endeavor, among other things, to draw a clear distinction between walking on level ground and walking up-hill.
I spent a substantial portion of my adult life being a frequent mountain hiker, until various musculo-skeletal troubles mostly shot me down 
I always found mountain hiking, as a form of aerobic exercise, to be vastly superior to walking on level ground, in various ways. These two activities – walking on level ground vs. hill-climbing – seem to be distinctly different exercises to me.
Walking on level ground, I always found that I had to walk very briskly – “power walking” or nearly so – to work up any kind of sweat sufficient to provide the cardio exercise I was looking for. (Yes, I always stopped frequently to check my pulse, and paid attention to the guidelines about what that should be.) This brisk walking seemed very stressful for my joints – the mild discomfort to my joints (which became worse than mild if I pushed it) was the limiting factor on my level-walking exercise, and it wasn’t good enough.
Contrast with up-hill walking: Here, the greatest effort in walking, by far comes from a factor not present in level walking: With each step, you put one foot forward onto higher ground than your previous step. Hence, when you put your foot on the ground, your leg is still bent (more than when you are walking on level ground). As you straighten your leg to take the next step, you are raising the weight of your body vertically, against gravity even if only by an inch or two.
This raising of your body against gravity is by far the most energy-intensive factor of up-hill walking, and is utterly absent in level walking.
The result was that one generally hikes up-hill at a much slower and leisurely pace than level-walking (if you are “power-walking” to get that cardio exercise), yet still getting a much more intense cardio workout. This intense cardio workout while walking at a slow leisurely pace, I always found, is vastly more comfortable to my bones and joints.
Up-hill walking, I am convinced, is also a totally different exercise: When you step forward onto higher ground and then straighten your leg, I feel almost certain that this intensely exercises different muscles, and at a different phase of the stepping cycle, than you get with level walking.
To get yet another very different exercise of very different muscles, try walking backwards up-hill. You will find that this is a very intense, and very different, exercise indeed. You can probably only do it for a few minutes at a time, even at your most leisurely pace.
This is exactly right. It’s not like the alternative to walking is just putting your body in a preserved state. Being sedentary is way more harmful.
Speaking as someone who’s been on prolonged bedrest, I think that most people have no idea how harmful being truly sedentary is. Even assuming you never want to go through the long recuperative process of actually getting back in shape (and all the stress on your body that it has), it’s bad for you in so many ways. Your cardiac muscle weakens. Your lungs become weaker and can’t function as well. And you don’t even want to know the horrors that bedsores can bring (and in a surprisingly short time). And this still wasn’t with zero walking - just with very little, on account of how weak I was.
It’s pretty telling that, today, hospitals are trying to get people up and walking faster than ever. My mom has had a knee and hip replacement and they get you moving pretty much instantly. Heck, they even put you on a machine to start moving your new knee back and forth before you wake up from the surgery. What you don’t regain in therapy pretty quick (in terms of how much you can bend it), you pretty much never regain.
When I was in the hospital – with autoimmune joint and muscle illness, no less – I was in terrible shape but they had me up and walking at least four times a day. I was so sick I could barely walk 50 feet, but they had me up, with a walker, and a person holding me with a gait belt in case of fall risk, because that’s how important it is to be up and moving. They also had me on physical therapy before they even started treatment for my disease. The PT told me that, in the hospital, they even get completely unconscious people to sit up, they move their legs around, even in some cases get them to stand – all while they’re in comas and the like – just because studies show how important it is to move, in nearly every situation. There are very limited and short-period exceptions to this, generally once you’re already on death’s door, but not in general terms.
Does it cause zero wear and tear on the body accumulated over time? Well, no. What exactly is an activity that doesn’t cause any wear and tear? Just being alive causes wear and tear. Time passing causes wear and tear. If you want to be pedantic, swimming might do a little less. But there’s no just ‘opt out of exercise for your health’ alternative here, and I really doubt that most people have the resources to swim nearly as much as they could and should be walking. At the end of the day, a knee replacement isn’t going to kill you but being sedentary sure as hell can.
I’ll second what fluiddruid just said: it takes a long time and a lot of effort to get back to being active after a period of severe illness.
In my experience, the people who complain about wear and tear on joints tend to be overweight. Being fat does put extra stress on joints, there’s no doubt about it. But, as we all (hopefully) know, being overweight is so incredibly bad for you on every level that a bit of extra stress on the joints is a small price to pay for losing that extra weight. If you’re so fat that your knees can’t support your weight, then you are in very serious trouble.