>What's the problem with recreational ingestion of nicotine? It's a light stimulant; I'm not sure why this is any worse than caffeine. And certainly isn't worse than other medications like opiates or amphetamines.

You're not wrong. But that's the problem - it's not enough to say "sure X is harmful, but so's Y, so it's alright". Ingesting nicotine by itself is a hell of a lot less harmful than taking it with tar and everything else that comes in a normal cigarette. But it's still a highly addictive substance, and personally, my concern is that marketing something highly addictive to the public (and, dare I say it, young people) is really seedy.