Such people will always exist, so there’s no need to pay too much attention to them. No one can guarantee that you will make a profit after just a few deposits. These people immediately blame the casino, but as mentioned, they soon realize that the mistake was theirs.
People should only gamble what they can afford to lose, assuming that they could lose everything, although there will always be some probability of making a profit. Gambling should thus be viewed as a form of entertainment. Also, given the nature of probabilities, as even the top poker players know, there will be at times long losing streaks.