Nobody is forced to accept his/her partner to be a gambler, because people have different views on this matter. But it's a must for everyone to be transparent and genuine to their partners. If they are gamblers, they have to openly tell this, so the relationship can grow stronger based on mutual trust, or the relationship can also end before getting too serious, due to the another side not accepting a gambler as partner.
Being transparent is very important and always avoid lots of problems in the future. If people were more sincere since the beginning of their relationships, we would see much less couples facing issues and divorcing later.
The issue starts because those who are gamblers know they are going to suffer from stigma and they are afraid they partner is going to see gambling as a deal breaker to them when comes to keeping a relationship with someone. So in the eyes of those who gamble and keep it secret, it is better just to avoid the secret to come out in order to keep their significant other close and not to lose them.
It is something which could only work
ofif the gambler gradually started to quit gambling, so their partner would never realize there was something hidden under the surface, otherwise if the gambler continues to gamble in secret, things are going to end up badly, as you said.
It is very easy to justify ourselves when comes to bidding information or lying because we assume we do it for our own good and the well being of our partner, but that is rather a coping mechanism for us not to admit we are not being as sincere as we are supposed to be... I have personally been there.