Do demo mode keep one from gambling addiction, what we can say for demo account is that it offer you pro information and insight into the real game but there is no reward system just as there is no financial commitment from the player, if you want to get the real drill and all that comes along with it you have to play the live games for some reason, and stake your own money, that is where addiction possibility comes in, if you don't control your urge at that point and situation.
Whether demo account or not, people gats to be careful in gambling because its doesn't seems to be it is, sometimes it acts to your wish and sometimes it doesn't and that is the power of luck, as it can protect you from the addiction, irrational decision and hurts which might ruined your lives and that of others. So for me, I don't really see a demo account to be any kind of help to me, as it won't teach me the things I really needs to work on like self-control etc.