Karl Marx was known, in part, for his idea that the most important work in today's society is done by the people payed the least, and vice versa. To elaborate on that, if all of our farmers decided to quit farming we would basically collapse as a society. Whereas if all of our stock brokers decided to quit how much worse off would we really be?... it's an interesting concept.

On-topic; Many of these issues (listed ITT) are intertwined immensely and to say that one is worse than another is just based on what you, personally, have been dealt in life. I don't imagine many of those are the actual answer to this.

Are drugs an issue? Yes, but what is more important than then the drugs themselves is why. Why are they using them? What is to gain? That is a much more important answer than just picking a drug and saying it's the issue.

Elk's thought, not having enough time for yourself, is something that I can agree with and see the logic behind it. But I don't think it's not having enough time. I think that we don't actually want time for self reflection right now. Many of our choices are not even really made by us (for example, when someone mentioned that going to college has become a must... most people don't choose to go to college for themsleves, they go because "that's what you do". The choice is made for them). Many of our choices are like this. That being, we didn't reach that conclusion ourselves and are just following what society and other people tell us to do.
I would argue that we don't want the time to reflect on these kinds of events and decisions, so we try and ignore it by distracting ourselves with YouTube, fidget spinners, ect. That works, to a point, to help us avoid examining our choices. This allergic reaction to self-reflection is a root cause of a lot of what has been said in this thread, I would imagine.
But this is not just a problem for this current generation, it's been a problem for a long time now. Avoiding choices has been a norm of human interactions for a long time now.

But, to be fair, if I had to pick a problem that is specifically tailored to my generation, it is our ability to hide in our intellectual safe-spaces of people who agree with us. I find it almost repulsive that we can't actually have legitimate political conversations because of this. I honestly think being overly ingrained in any belief to be a bad thing, and this issue is only getting worse. Now I can even make my news display only ________ political opinions. People hold onto their beliefs like hell, and now that we can hide ourselves from the other side we don't even need to know how to defend our beliefs... after all, in my safe space no one will ask me to explain why I feel the way I do.

Not to single you out, but what you're saying is a perfect example of what I said above... you're saying that smoking itself is the issue, and it is not. If you had a magical wand that could remove smoking from the world we wouldn't be any better off than before. If the underlying causes still exist they'll just move onto some other addictive or destructive habit...