Very good question!
I have been playing poker online for several years, as a fun hobby, and also as a way to make a few extra bucks. I have been playing Texas Holdem for years, and online I only play NL holdem tournament poker in multitable games. I am also a USA player, so my answer is pretty much limited to that area and the sites that offer poker online. And I know a lot about that subject, lol.
I also know quite a bit about gambling in general, in years past I was a frequent visitor to Las Vegas, and played a lot of blackjack and craps. Most of the other games I avoided due to high house advantage.
FIrstly, there are many many online sites that are BAD! Some of them are little more than scams, and here is a link to an online casino BLACKLIST. Teenage students? Most sites require you to be 18, and to get your cash out you must prove it with ID. If a teenaqer under 18 wants to gamble online, then I suspect it is not that hard to get around these rules with some fake or borrowed proof, my daughters have told me how easy this was to get. If someone is over 18 and a student, they most likely do NOT have a good understanding of the odds involved in the games or the slots, so they are mostly taken advantage of.
Is it serious problem? Maybe for some. There is no regulation of most sites, and they operate under different countries laws, which means there is little if any recourse for dispute resolution. If you can avoid the scam sites or the underfunded sites ( many have folded owing players lots of money, ie, Jungle, OKUSA, Tropical, Wingows, PokerDream, etc), the cheating scandal sites (lots of those) you can have some fun. There are USA legal sites that you can play for FREE and still win prizes or cash, or play for a small monthly fee and win some big cash prizes.
Since these sites limit your potential losses, this is a safer form of playing online poker, still getting the poker experience and maybe being able to win some cash.
It can be a serious problem if the player becomes hooked, or the gambling becomes an addiction, and this can happen online, since it is so easy to login and play. But then a certain percentage of players will become hooked no matter what, at live casinos or in local games. Online play does make it easier to be come hooked.
Colleges, or all learning institutions, in my opinion, should offer courses on gambling! On how to understand the odds of what gambling you are doing, or what you are playing, so that students will be prepared for the real world. Most new young players have no idea about how gambling works, and a pre-education could help them avoid future losses.
It is not the reponsbility of the casinos to screen users, except for meeting age requirements, it is their responsibility to offer a fair and honest gambling site. Many of them do have ways to limit your loss exposure. But like the B&M casinos, online casinos are in business to make money, and they will take money from as many players as they can get to signup and play. If there was a form of legitimate regulation for online casinos, then there may be a way of controlling the screening of users, and ensuring this would be done.
Bottom line? In my opinion, online poker (and gambling) is still an area with many pitfalls and even dangers to players. While many of the bigger more reputable sites, like PokerStars, Full Tilt, are most likely to be safe, we have seen some big names like Absolute and Ultimate Bet with major insider cheating scandals.
Online poker needs to have a legitmate form of regulation, control and enforcement to be safe.