1) Gambling brings you loneliness, or makes you feel alone or want to be alone, it can isolate you from society or from other important events in your life.
2) It can suck your energy or your happiness, it can get inside your head and won't leave you alone until you gamble again.
3) Not to mention it can can destroy you financially, you can lose a lot of money in a matter of seconds/minutes/hours/days. Some stories show how people lost over millions of dollars in a matter of hours or days.
4) Gambling can also destroy you individually, not only financially, you can lose your family, your job, your friends or relatives.
All these happen in the case somebody gets addicted. Then indeed, he lose the control over his life and money.
But this kinda happens with all kinds of addiction.
I think that the easier summary would be: the disadvantage of gambling is that it can trigger too easily an addiction.
But again, a lot of addictions fall into this "too easy" group.
So.. yeah.. everybody, don't gamble more than you afford to lose and gamble only while it's fun.