The next logical step would be to ban cigarettes, but allow people to continue to purchase loose leaf tobacco. But if that happened then smoking rates would likely fall enough that it'd no longer be a major health issue, so even if we are in a slippery slope situation it doesn't seem likely to me that criminalization is the logical conclusion.

Already most smoking deaths are in long term smokers. The 14% of Americans who still smoke are for the most part only smoking a few cigarettes per day (except the couple percent in the severely mentally ill population), so they're going to have nowhere near the same level of health outcomes as the folks who spent decades smoking multiple packs per day. I wouldn't personally ever use tobacco products because I place a high value on not being dead, but from a statistical perspective just looking at the number of current deaths would lead one to vastly overestimate the risks of tobacco use practices. I guess my point is that from a personal level you should definitely not smoke, but at a public policy level we'd hit the point of diminishing returns far before instating a complete ban.