Business is business. The tobacco company approached Juul, not the other way around. There is some price where the early investors will sell. That's why they invest. One possible good reason for Juul to have a very large corporate investor is easier access to cash to pass the FDA pre-market requirements and the early investors get a pay back even if Juul is not approved.
I started smoking as a kid, of course. I blame government for that, not tobacco companies. If there are no tobacco taxes on ecigs tobacco companies might make larger gross profits on smaller sales than they make on selling larger amounts of heavily taxed cigarettes. I have no problem with that even though I don't anticipate using their products. It wouldn't be all bad for tobacco companies and vapers to have some common objectives.
A trend I'm only noticing recently, because I've been focused on other things, is the popularity of pod systems. Several stores I've visited say they intend to phase out the hobby vape stuff and focus on pods (which doesn't change my life since I buy everything online). I'd get a pod to see what all the fuss is about but there are too many to choose from and I don't know what to get.