The links from John Hopkins, the CDC and Harvard all focus on vaping, and so are irrelevant to the question of nicotine rather than the delivery methods.

The first link has nothing wrong in it. It's correct nicotine is toxic. So is caffeine - the LD50 of caffeine in humans is reasonably high, many grams. To the issue of ingestion, the issue is toxicity at doses people are likely to deal with.

To the cancer links, again without looking at delivery methods, this is meaningless. To let me quote one small part:

Thus, the induced activation of nAChRs in lung and other tissues by nicotine can promote carcinogenesis by causing DNA mutations[26] Through its tumor promoter effects, it acts synergistically with other carcinogens from automobile exhausts or wood burning and potentially shorten the induction period of cancers[43] [Table 2].

This makes sense. Don't inhale lots of particulates combined with nicotine in other words. There are also many other parts of the article that are useful. E.g. it's perfectly reasonable to accept that e.g. if you are on chemo you should stay off nicotine, and if you breastfeed you should stay off nicotine.

What the article does not show is that nicotine, as opposed to delivery methods like inhalation, is much worse than other drugs we're perfectly fine with.

I'll note that the article also includes things in its conclusion that it has categorically not cites studies in support of. E.g. it just assumes the addiction potential is proven (it is, but putting that in the conclusion of a paper without citing sources is really poor form, especially in a paper claiming to set out the issues with nicotine in isolation rather than smoking).

It also tried to drive up the scare factor by pointing out its toxicity at doses irrelevant for human consumption (e.g. as an insecticide; if wildly irrelevant doses should be considered, then we could write the same paper about how apples should be banned because they contain cyanide).

The "Materials and methods" section also goes on to say "Studies that evaluated tobacco use and smoking were excluded" but then goes on to make multiple arguments on the basis of harm caused by smoking (e.g. "Nicotine plays a role in the development of emphysema in smokers, by decreasing elastin in the lung parenchyma and increasing the alveolar volume") and cites a paper focused on smoking, in direct contradiction of the claim they made ("Endoh K, Leung FW. Effects of smoking and nicotine on the gastric mucosa: A review of clinical and experimental evidence. Gastroenterology. 1994;107:864–78.")

So, yes, if you make claims about how you're going to address nicotine rather than smoking, and then go on to address smoking and other means of inhalation intermingled with the rest, and if you leap to conclusions you've not cited works in support of, and if you throw out risks without linking them causally to nicotine, you can make nicotine look very bad.

They also end with subjective statements they've not even attempted to support properly. E.g. they've gone from "here is why it's dangerous" to "it should be restricted", but if that was valid logic, we should restrict sales of apples too, most cleaning agents, all caffeinated products, housepaint, paint thinners, and a host of other things, it's a specious argument and fitting that such a badly argued paper ends with it. That this passed peer review is an incredible indictment of the journal which published it.

That doesn't mean nicotine is risk-free, but compared to other things we're happy to ingest, I stand by my statement. But don't inhale it.