The negative effects are what the gambler know before start gambling but because of greed and addiction they keep playing gambling. Some desiring to stop gambling but they could not because of addictions. Few are actually succeeded in gambling and that is the reason we should not blame the gamblers as they also wish to succeed.
You don't know the exact effects of gambling before you start playing.
You may have heard them before but it is different to hear from others experience than noticing by yourself. This is why more and more people start gambling and getting greedy as they play more. The feeling and the excitement of gambling brings the effects.
Maybe but at least you should know the risk in gambling.
We don't really need to experience in order to know, we have other people who are kind enough to share their experience, I think we can learn from them.