Oh it was definitely a slippery slope argument, in the form of an analogy. You analogy went as far as saying trash and mail are the same, you are aware of that? Clearly, that is absurd and is using a case of an extreme. Mixing trash and mail, or trash and recycling, and sorting them later is obviously an absurd process. Mixing bottles and cardboard in one recycling bin is not absurd. But your analogy was clearly attempting to conflate all of the above, and I'd be going easy on you if I didn't bother to point that out.
Clearly the Bookmarks "star icon UI" is physically located in the omnibar, but when I said "settings and bookmarks", that clearly wasn't what I meant- I meant modifying the settings and bookmarks through typing a command in the omnibar the way you'd type a URL or search query. Bookmarks are not in the omnibar the way you can type "INSERT INTO bookmarks SELECT current_website FROM current_window" into the omnibar to add a bookmark. You can't change the settings "UPDATE settings SET setting_value=black WHERE setting_name=theme" by typing into the omnibar.
However, neither of my previous 2 paragraphs really refute any of your points, they're just clarifications. Pointing out that you made a slippery slope fallacy in an analogy doesn't refute your point, and whether Bookmarks are considered "in the omnibar" or not is orthogonal to the discussion. I agree wit the paragraph on "the true original sin", but that's a different note as well.
So, returning to the main issue: I think the cost issue is a valid point, but then everything has a cost. Even putting bottles and cans in the same recycling bin would incur a cost. Then the end question becomes "is it worth incurring this cost?". For a lot of people, they are willing to pay the taxpayer cost to have their recycling be sorted between the bottles and cans and cardboard etc. Do you have a separate recycling bin for glass bottles, aluminum cans, plastic bottles, cardboard, etc? Or just one recycling bin? Similarly, there is a cost to giving google a tiny bit of additional information- but not much. Plus, they already have your entire browsing history stored on their servers already. Try going to some webpages on Chrome, going to a different device, and check the browser history on the 2nd device- it'll be synced with the first device. So on Chrome, there's no additional privacy cost to combining the url and search bar. Even if you use firefox, there's not a lot of information being leaked with the omnibar that accidentally googled something that was supposed to be an intranet site. For the consumer that doesn't know the difference between a URL and a search, they probably aren't running some sites on their local network anyways.
Considering how low the cost is, I'd say a sizable chunk of people who oppose merging the address bar and the search bar do it out of a purely principled stance where they cannot accept any cost greater than 0, not even 0.00001. I'm not sure if this is a logical position to take, although it makes sense as a philosophical perspective, at least. The other chunk of people are just using it as an excuse to back up a philosophy of "people who are lazy do not deserve our sympathy", which makes even less sense logically (again, see: brain surgeons, grandparents) or philosophically.
On that note, I absolutely hate the quote "the only intuitive design is the nipple; after that, everything is learned". It's one of those cynical quips that just makes the person saying it seem smart, but actually leads you away from the truth. People massively overestimate the concept of a tabula rasa, and not all knowledge is learned. One example I can use against (a good percentage) of tech people is exercise at the gym. If you've ever done squats/bench/deadlift, you know the importance of having a good form. If your form is wrong, it will "feel wrong"- this is something that even absolute beginners at a gym notice, even if they don't have a trainer telling them exactly what is the right form. Another one, (a more interesting subject on the state of the human brain), is observing how people react to certain drugs like acid. Amusingly, novices to psychedelics are always convinced that whatever thought they've just come up with is some groundbreaking revelation, when it's usually something that's been thought of many times before.
> such as that I need to walk more every day--I don't prioritize doing it
Isn't this inherently more lazy and/or worse? This would be like someone who knew what a URL is, and then purposefully choosing to search up items in the Firefox URL bar anyways. At least not bothering to learn is excusable- again, I don't really need my brain surgeon to know how a URL works and understand making a DNS query for an infranet site works. But philosophically, this seems like throwing your trash in your mailbox and being okay with it because it would disappear anyways (excuse my slippery slope analogy, heh). And also I can possibly argue that you don't know that much about your health, anyways- for a human body to stay healthy, it needs more than just walking. Putting heavier loads to build muscles (maybe not specifically for hypertrophy, but certainly not just LISS cardio) is important, especially for your back. Also, sustained high intensity cardio is important for your health as well.