Your post made me think that that bank did not care much about that person and personnel in general. Few fails at work, caught gambling - got fired. In someway I think it might be more human to try to help that employee with his gambling. I dont think that bank fired him immediately when they saw him gambling for first time. I think there were talks, warnings before firing that person. If they see a person has problem, it would be best to help him. Instead, now he still had this gambling problem, and now he is jobless in addition. Bank made his situation from bad to worse.
I don’t think the bank should be accountable with what the gambler currently experienced now. The fact that the employee is no longer productive in his own job, regardless of its reason, then the employer have all the right to warn or worse fire the employee. But of course, this doesn’t happen in an instant for sure. Most probably prior investigations or interviews from other employees have been made first. Until proven that the employee is no longer effective in his position, then the bank should call out his attention or fire from his job.