I see no reason giving out loans to a friend who is not credit worthy, no matter the situation the person is in and the level of relationship that exists. A person who has a very low income should work hard to increase his income. If he thinks gambling is the only way out, then he is just being lazy and irresponsible. Even if he must gamble, he or she should at least work for the money he will use to gamble, instead of being indebted to lots of people.
If you know a particular person is a gambling addict and you still go ahead to loan them money, you are not only putting your money at risk, you are also making things worse for that gambler. An addicted gambler needs help to recover from his addiction and not more money he will not use well. If you feel compassion for his suffering state, help him recover from his addiction.
In that aspect you are absolutely right, I don't see any good reason to lend money to a friend who has gone too far in gambling and who already has some history as a person addicted to gambling, it is difficult because there can be a strong bond like friendship, but sometimes friendship must be separated from business, from money, and even more so when there is some uncertainty about your financial situation and how it can affect the relationship later, sometimes friendship is damaged by incidents with money, and well, that's not the case. It's a very good design, sometimes it's hard to say No to a friend and tell them the real reason, because I know they won't take it well, but sometimes it's for the good of that friend.