It is also readily apparent to me that nicotine is bad for us, generally and broadly.

The combination leaves wiggle room for nicotine to be a net-good lever on certain mechanisms. I do think it's best to avoid it; It's a challenging double-edged sword.

The molecular biology of how it's maybe-good and maybe-bad is probably the most useful aspect of it. It's a strange sort of bronchodilator and has weird and ambiguous antiinflammatory properties. (Which seem to tie in to how it is addictive: Short-term bronchodilation and oddly-shaped short-term antiinflammatory properties turn into bronchoconstriction and proinflammatory effects as time passes from taking nicotine, which feels like it would be rather inductive to generating a craving for more nicotine.)

Re. Parkinson's: Wild guess, addled brain hunching on nebulous perspectives, but I do think that nicotine's protective effects against Parkinson's are indeed related to the bronchodilation and antiinflammatory aspects, and more specifically it seems to me that Parkinson's has pulmonary basis. I think we're nuking our lungs in many subtle ways that in some of us cause the dam of cell death in the substantia nigra to break. How might we be nuking our lungs? Say… Air pollution, incl. microplastics and plasticizers, various disruptors of fine pulmonary epithelium and metabolic function and neuroendocrine autonomic control. And I'd think that once we start to lose fine autonomic control by way of loss of dopamine cells in the substantia nigra, we'd be poised to enter a vicious cycle of further loss of pulmonary foundations.

but idk, just sayin lol