From the general public's perspective, gambling is often considered a negative activity and not good if done excessively. Furthermore, taking out loans solely to gamble is clearly very risky. Even professional gamblers can't always win, as gambling doesn't guarantee a return on invested capital or the possibility of winning many times over.
It's those who overdo it and experience its negative consequences that make gambling a negative thing. If more people gambled wisely, I don't think gambling would be viewed negatively. But the reality is that more people do it excessively, even though it's clearly just a form of entertainment that won't have any negative consequences if done in moderation.
Given that gambling carries obvious risks, we should know not to overdo it. However, those who experience these negative consequences may sooner or later realize the need to stop gambling excessively and try to be more judicious in their dealings.