R’ Yehuda says that both mesahakei de kubla and mafrihe yonim (people who gamble by wagering on pigeon races) are pasul when this gambling constitutes their sole livelihood. The mishna (Sanhedrin 24) says explicitly that people who have a profession and aren’t professional gamblers are not pasul.
Rashi explains that the professional gambler (as JF02 says) isn’t involved in improving society or doing anything useful, and as such, they have no familiarity with business norms, and have no aversion to illegal activity.
In the gemara, there is a machloket R’ Sheshet-R’ Rami bar Hama on why the dice playing makes the gambler pasul. R’ Sheshet says they’re pasul because they don’t contribute to society; R’ Rami bar Hama says that they’re pasul because gambling is an asmachta,(the loser did not resolve to pay if he loses, for he expected to win, and as such, the one collecting money from the bet is stealing, which makes one pasul). For R’ Sheshet, being a gambler is operatively what makes a gambler pasul (he says gambling is not an asmachta, because to be an asmachta, the player has to rely on their own ability, and a gambler is knowingly relying on chance, not ability).
Rif and Rosh both say explicitly that a dice player is pasul due to the fact that he doesn’t contribute to society. The Rambam says that gambling, even when it is stipulated that the winner will take a particular amount, is gezel me d’rabbanan (even if the owner lets the winner take, the winner is collecting for frivolity, as this is gezel). Rambam therefore forbids all gambling, not only professional gambling. And gambling is generally believed to be a davar mechu’ar (Rivash paskens as such), even if you don’t hold like Rambam (and R’ Rami bar Hama that gambling constitutes gezel).
Rabbi Wallerstein’s comments hold correct in a certain sense; gambling is a bad thing, whether you hold le ma’aseh like Rami bar Hama/Rambam, or Rif/Rosh/R’ Sheshet. Whether you hold that a gambler is pasul due to the act being gezel, or due to the fact that a gambler is a miscreant, certainly Judaism views it negatively.