I fully agree with you, the ones who borrow money to solve some of their financial issues or to buy some food for their family is good use of borrowing but it's not good at all to borrow money for gambling.
If someone becomes an addict then in most cases no one lend money to such people but if still somehow they get success in borrowing money then it would be problematic for both the borrower who gambles it away, and for the lender who might not get his/her money back.
It's not like no one doesn't want to lending money to a gambler, it's more like lending money to a gambler that doesn't know how to pay back. Some people have this sweet mouth to request for money, they will make you all sort of promises to pay back but as soon as you gave them the money, you will be the one to be running after them to pay back and since debt isn't a police case, you don't have any power to hold them unless you charge them to court and that doesn't make sense.
If a gambler comes to you for money and you have the money that you wish to give, you should give them but never expect them to return it. If they return it that fine and if they don't that's still fine because you have already made your mind from beginning that you aren't expecting the money from them. That's the only way you can be free from any friend that is a gambling addict.