What is gambling? Gambling is certainly a game but it involves money thats why one should handle/use it responsibly . Investment? Uhm, Yeah if you have a decent amount of money you can invest to a gambling site and you will be called a investor but for someone who just plays gambling it will not be a investment cause you're just a player not an investor .
Yes, it's kind of games involving many risks. Risks to lose money, to become addicted, to waste much time of your life... The high risk when gambling makes the game interesting for most players and allow the game to offer very generous money offers possibilities.
As you said, we must play this game with responsibility, carefully, to prevent big losses that won't give us any benefit. The advice is, play for fun, use the money you are afford to lose. Don't forget that there is more interesting things to do in your life.