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.
The only reason the recycling examples seem absurd is because 1) it simply isn't that difficult to remember "trash goes in a black in and recycling goes in a blue bin and mail goes in... a different blue bin ;P" and 2) it is obvious how hard it is to separate the two results in the general case and the ramifications seem silly to tolerate given the low effort that the user has to take on to prevent it.
The exact same thing is true of the omnibar: there are a bunch of heuristics that often work well enough and people who are particularly lazy and don't want to learn the difference between the various bins don't have to because we figure it out for them... most of the time. I personally think that people shouldn't be so lazy, but it seems like the entire goal of "UX design" is to empower lazy people to "not have to think" (which is very different from "intuitive": after all, "the only intuitive design is the nipple; after that, everything is learned").
The reason then I think it is "destructive" goes further, though, than "people who are lazy do not deserve our sympathy": it is because, as someone else pointed out, there is a cost to leaking a user's intent to the search engine when they wanted to type in an address (in the same way that mailing someone's trash out randomly might be a privacy violation). Google doesn't give two shits about this: they want all of your information. That Google is training people to conflate the process of searching for something with then process of navigating to something is great for them and sucks for Firefox as Firefox kind of has to follow or be screwed and yet it seems a bit antithetical to their mission (though I don't think they even know what their mission is anymore).
(FWIW, the true original sin is the address bar itself: the address bar is a status display of where you are... making it editable is arguably sort of "intuitive"--using the typical kind of "just so" stories that allow people to claim random things are intuitive because the story was flowery enough--but frankly it just makes no sense and causes all kinds of problems. If you fix this, and return to the paradigm that some of the earliest browsers have, I think some of the other things the omnibar does are less awkward, and the "out" for true navigation wouldn't be affected as navigation would feel entirely unlike searching: it would become intuitive that these are separate concepts.)
(Also: the fact that I am unhealthy is not because I don't want to know how to be healthy or because I am not prioritizing understanding it... it is because most of the time I can't for the life of me figure it out even in consultation with doctors, and when I do know things--such as that I need to walk more every day--I don't prioritize doing it because I injured myself a couple years ago and I am now somewhat depressed over it. I point this out because it is very different from not knowing or not caring to know: a life un-analyzed and without curiosity at every level of scale and in every interaction would seem to me to be a life wasted. If you truly don't know anything about how a car works, I recommend spending some time to learn: it's fun! Tim isn't like the mechanic ever figured out what was wrong with my car until I finally pulled the error code of the ECU myself and rubbed it in his face. Learn to play at least one musical instrument of every class so that you can extrapolate the rest. Study linguistics as early and as often as you can in life so you can at least appreciate the beauty of other languages even if you don't choose to become fluent. Avoid hiring people to do things for you until you know how to judge if they did a good job, and decide how you wish things to be done before letting other people tell you what they like and then don't back down!)