re. nonsense, paragraph per paragraph:
1) biking is more energetically efficient than walking.
2) eating any kind of meat daily is not sustainable in the long run, and thus not intelligent (which does not prevent me from eating some, from time to time).
3) You ignore the notion of sustainability. Having some impact does not matter, as long as you stay beneath the sustainability threshold.
4) Your 100 / 110 ratio seems to come out of nowhere. Do you have any data to support it?
I presumed my parent was not primarily concerned with sustainability due to bits like dead orangutans and I like beef, but I sympathize for a fellow mammal. Sympathy and orangutans are not really part of the sustainability picture, which is a separate and large issue I don't intend to dive into right now.
Eating meat can be sustainable. I'm pretty confident if we all ate crickets, there would be practically no sustainability concerns, and we can't all eat quinoa as our protein source anyway. Chile is not able to grow enough quinoa to feed the world (quinoa is a picky plant)
The 100 / 110 is purely invented as a thought experiment, but I consider it to be representative. Your daily BMR is ~2000 Calories. Engaging in activity, sports, games, or mental exercises do increase your caloric consumption for the day, but your body adjusts quickly and your additional caloric consumption for the activity falls quickly into the hundreds of calories for all but the most strenuous activities. Plus, the more strenuous (calorie-expensive) the activity, the more likely you are to take rest days, which lowers your average daily caloric consumption.
Some levels of externalities are sustainable. Some are not. The larger problem with humans is the combination of total population and average per-capita resource consumption (to say nothing of the vastly higher consumption in industrialized nations).
The steel and rubber in a bike are probably the biggest concerns (as well as the paving in roads), but in comparison with an automobile, it's vastly lower, and in comparison with the ranges and cargo capacity of walking, they're hugely higher. I've travelled 200 miles in a day by bike, and commuted over 40 miles daily for over a year at one point. One person on a bike can move a payload of many hundreds of pounds, possibly a ton or more (across level ground).
Food production at present is manifestly unsustainable. Every one calorie of food you eat in the US takes 10 in fossil-fuel energy to produce (in Europe it's about 5). Other inputs, particularly nitrogen (from fossil fuels) and phosphorus (limited global supplies) are crucial limiting factors, as are topsoil and water.
Richard Manning's "The Oil We Eat" is a fascinating exploration of this aspect of human existence: http://www.wesjones.com/oilweeat.htm
2. Sustainability is what matters.
Does this activity add to the likelihood that humanity will cease to enjoy a standard of living similar to the current average at some point before other natural processes (Sun going red giant, etc.) kill us all anyway?
So hey, if they sun's gonna kill us all next year, go hog wild. If what I'm doing now means that somebody 500 years from now will have a more impoverished existence, it's not.
Advanced species lifespan seems to range from ~1 - 10 million years or so, plus or minus a lot, before genetic drift sets in.
Three hundred mega-years (what I meant) is a somewhat arbitrary milestone. (I think long-term but 10^15 years is a bit much for even me. But see Stapledon's "Star Maker"...)
(BTW, your thinking seems unusually clear on these matters.)
None of these are good, but we don't eat pandas, so which examples of habitat destruction are used is informative.
Yes, telegenic megafauna capture hearts, but really, as apex predators or other apex species, they're the canaries in the coal mine, so to speak (and my isn't that an unsustainable metaphor...). But the waste being laid to oceans: 80% depletion of fish stocks, mass strandings of numerous cetaceans, algae and jellyfish blooms, starfish wasting diseases, and the sudden disappearances of birds, seals, and sea lions, all suggest something is going very, very wrong.
And those systems are crucial for life on Earth -- human and otherwise.
I KNOW. But, difficult as it may be to believe, sustainability still isn't what I was talking about. And, no, that doesn't mean I believe it isn't a problem.
Also, did you read my parent? Parent was not talking about sustainability and burn rate vs. incoming solar energy or production rate. Parent was talking about mental anguish brought about by the costs his existence poses on the planet- at least, that's what I heard.