Some of what you say here is true but that doesnt mean gambling will ruin your life. If you have an addictive personality and cannot control when to stop gambling, then yes you prob shouldnt gamble. If you have self control and just wanna toss a few dollars around here n there then youll be fine.
Self control in my opinion can be gained before you gamble or even after you gamble. On the other hand self control can also be gone during the time that you gamble that happens when you already are addicted to it. Although you are right as well because in the first place we gamble to release stress
Self control is something that will make you gamble on a discipline way during your gambling session, it is not after but it's during your gambling session. Having that kind of skills, you will be able to execute your game plan very well and most probably it will lead you in the winning track.
so its not quitting its just another way to have some good earnings or lessen your risk, its still much better to quit if you are not really into a gambling activity and you are not aiming to be a pro, those who have self control are the ones who can them self as a pro in that particular fields.