1 Thessalonians 5:22:
"Abstain from all appearance of evil." (KJV)
The idea here is that as a "Christian" one should be careful about appearances, as you may stumble someone against accepting the "truth" simply be creating the wrong impression. It is not merely the avoidance of evil, but avoiding even the appearance of evil.
Suppose, as a JW, you knocked on the door of a householder last weekend. He/she invites you in, and you have a nice discussion, as a minister of Jehovah. You share this JW message about having the "truth", and how you let the Bible be your guide, and you talk about the end of this "wicked system of things" which is soon to come. This householder listens with intense interest, and you see that he/she would be an excellent candidate to start having bible studies with.
Now, this same person, who felt this high degree of respect for you as a representative of Jehovah, now sees you in this gambling establishment. This householder thinks to himself/herself,"What's this minister of God doing here doing in a place like this, if he/she is supposed to be Christian? Well, that looks like a hypocrit to me, so I don't think I am interested in further conversations with that person, if that's the way these JW's are!"
Do you see how easily this can be a cause for "stumbling"? It is all about the "appearance of evil", which must be avoided.
I remember when I was a JW back in the 1960's that we had a lot of discussion about this whole topic. One of the fellows back then told me another incident that might happen. Suppose I was at the Kingdom Hall, and I saw a brother wearing this loud tie that really bothered me. Then it would be the duty of that brother, in a spirit of humility, to not wear that tie, lest it be a cause for stumbling of another Christian brother. The Apostle Paul had a number of comments about this, but I don't recall which scriptures they were in the New Testament without doing some research. But they are there and they are pretty plain.
Gambling and casinos are filled with people who are into drugs and prostitution and all kinds of evil and worldly things. Legs are broken, even murders committed (putting contracts out on people) who do not pay their gambling debts, etc. Many lives and families have been destroyed or ripped apart over gambling. This is the real world of the gambling environment. Would a true minister of Jehovah want to create a wrong impression about spending their time in such environments, rubbing shoulders with bad associations who are steeped in this worldly wicked system of things of whom Satan the Devil is its god.
Now, having left the JW's many years ago, I no longer subscribe to all these premises. I am simply trying to get across the point that if you choose to be a true JW, then you must not, at the same time, spend your time in such establishments to save a few bucks on a meal, when doing so runs the risk of stumbling someone who might otherwise see the "truth" by your Christian example.
Rod P.