Addiction and greediness walk side by side, but if we have to say which one is the most harmful, I would say it's addiction, because it implies a more compulsive and disastrous behavior from the individual, what means he acts without thinking rationally, logically and thinking on the consequences of his acts. Greediness solely, on the other hand, might mean the individual is avid for profits and wealth in an extreme manner, although it doesn't imply he acts compulsively for that reason.
Actually, he may act rationally and logically in order to achieve his greedy goals, being a successful businessman, entrepreneur, investor and so on... Greediness doesn't necessarily prejudice someone's skill to make money, while addiction does.
I would also go with addiction as the more disastrous one. Because most addicted gamblers won't stop even if they have no more funds to spare in their gambling activities. So they resort to taking loans and other worst scenarios such as stealing. Whereas, with greediness, the gambler may still have the awareness of stopping his habit. Sometimes he just wants to continue his games despite of winnings.
Greed is a trait and addiction is a cycle, meaning that in this case I cannot separate greed from addiction, because greed is something that can trigger addiction, meaning that these two things will go hand in hand where greed is the initial trigger, And if we talk about addiction then yes of course that is a bad cycle or zone that can cause a variety of much worse impacts that we never thought before, these significant impacts occur as a result of a gambler who makes various actions and decisions that are really aggressive, one of which is like what you said that they are even desperate to justify all means just so they can get involved in gambling.
Whatever they will do, especially borrowing money from anyone with various reasons based on lies so that others believe and give loans that they can even do other worse things like what you said, namely stealing or robbing or cheating others. And as I said above that greed is still a trait that humans have and what is called a trait is a habit that they often do, meaning that although awareness is still a possible thing to achieve but I think it is very unlikely when it has become a habit.