I have a big enough problem already with brick&mortar casinos, I think they're a big rip off and a waste of time and money: for the user there is no positive side even in the medium term really, certainly not in the long term. However, there is a civil liberty issue: people get excitement from doing it (to the point of addiction), and they want to do it, and technically speaking (tongue in cheek here), for certain people it can be something they can keep under control (but if they think they're gonna make money from it they are totally mad).
I'm rather see them all gone, I'm glad we didn't let the super casinos in, and I think the USA did the right thing in effectively banning all online casinos. You just cannot let this kind of thing into people's homes, it is too easy to get addicted to them, and too hard to control people's losses for them (like a real casino could/should).
Having said that (lol), I have been in a lot of casinos and a lot of gambling sites (I used to play poker professionally and still put in a couple of hours a day, and made good money from it: but it's not gambling for the most part, mainly skill). Even poker though can become a big loss making activity for many people (most don't know what they are doing). I'd rather see the whole lot shelved.
I mean: a controlled heroin habit does less damage than a hardcore gambling problem, but that is banned 'because of potential harm'.