As to the first question on the harm of nicotine, it is both an extreme poison and about as harmful as caffeine. As with most things in medicine and nearly all drugs, the dose is everything. In the dose tobacco/nicotine users consume it appears to be about as harmful as caffeine. If it is more harmful it is not by much. It is also true that a drop of two of pure nicotine on the skin will very likely kill you. Taking two aspirin is therapeutic, while consuming a whole bottle is very toxic. It's not either/or, it's both.
As far as reducing your nicotine level the question is why. If you are contented with a certain level what's the point of reducing it to the point where you are having problems. Unless your plan is to get off all nicotine just stay where you are. If you do plan on quitting all nicotine (which I don't) that's a whole other question.
Different people react differently to nicotine, just as people react differently to alcohol, caffeine, etc. For some it is highly addictive (and I might add beneficial), and for others it has little effect. Some can easily quit nicotine while for others it is nearly impossible. Welcome to the human race.
Yes. What you said. Absolutely.
Sure it's "a poison". In fact, starting around the 17th century, it was used as a insecticide. Use peaked around WWII but by the 80s, it was rarely used anymore. Then in 2008, the last registered user requested a cancellation of their registration and apparently as of next year, nicotine insecticide will cease to be available at all in the US.
Nicotine - Wikipedia, the free encyclopedia
But anything in excess can be deadly. Water can be deadly. Not just drowning in it but it's actually possible to get "drunk" on water. You have to drink
a lot but every so often, some idiots who heard they could get drunk with plain water put themselves in the hospital trying for a cheap drunk. You can even kill yourself throwing your electrolytes out of balance like crazy making a serious mess out of your brain chemistry.
Ah, here's a bit about it:
Water intoxication
And folks making the comparison with caffeine should maybe consider that... wait for it...
"In plants, caffeine acts as a natural pesticide that paralyzes and kills many insects feeding upon them."
Caffeine
Seems we humans like what small doses of poisons do to us?
My grandparents were married at the very bottom of the Great Depression. They knew truckloads of "home remedies" for all kinds of things (wish I'd gotten more of that from them before we lost them, not all of it works all that great but some can really save you money). But I was griping about ant hills once and was told to dump coffee grounds on them.
I don't know if it kills them or repels them or a combination but they go away.
But people do react to things differently. When I was younger (and we rode dinosaurs to school

), I used to think people were full of it talking about "caffeine withdrawal". I mean, come on, it's just coffee. Addicted? Yeah right.
Reason I thought that was I don't seem capable of being addicted to caffeine. I enjoy my morning coffee and do it every day. But if I get up and the cupboard is bare because I forgot to pick some up, I just add it to the grocery list. No headache, no jitters, no... nothing. And I'm not just switching caffeinated drinks. For one, I never have liked sodas. (Well, okay, when I was a kid, I liked root beer floats. Back when A&W had stands on every corner. But that's like, centuries ago now.

). Coffee is the only caffeinated thing I ever have in the house.
So I have no idea what it's like to go through "withdrawal" with caffeine. After college and the "all nighter" thing, I kind of lost interest in coffee for a while. Just stopped. Nothing happened.
Kind of wish it was the other way round. A caffeine addiction seems not to beat up on your health quite as much as cigs do. But, well, reality is what it is. At least this vaping (is that right?) seems to be a better way to get the nicotine than tobacco. Dunno about "safe" but I'll take "safer". And maybe I'm fooling myself as it's been just a handful of days but I could swear I have a bit more energy lately. Getting more oxygen than I used to maybe?
Dunno. Hopefully it's a trend though...