I like to consider myself a moral person (and I think most people that know me well would prob agree, I hope!) and I have no moral compunction about playing for a living.
The basic reasoning is this: poker is a state-sanctioned game with well-defined rules and all players are willing adult participants. In other words, the game is legal, follows established rules, and is played by consenting adults. Professional poker cannot be reduced to an immorality by definition when none of the essential components of the game itself are immoral.
But the whole question is often unnecessarily complicated by the fact that a lot of things associated with poker (professional or not) are evil, corrupt and/or illegal. I think this is kind of inevitable when you have so many people participating in so many transactions involving transfers of wealth.
In case no one has thought of this analogy: trading of stocks (I guess derivatives might work better) is a zero sum game, just like poker. And, just like in poker, there are transaction costs (rake, tips, etc), professional/institutional traders (grinders) and individual traders (recreational players). The presence of immoral activities/participants in stock trading doesn't make the profession of stock trading definitively evil.
This isn't entirely on point, but I actually think poker as a profession probably requires a higher standard of morals/ethics than a lot of other jobs with comparable skills and pay. But I could be slightly biased
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As for the societal/economic value of professional poker, it's closely tied to the value of the game of poker in particular and that of the entire casino industry in general. One way to think about this is to consider professional poker as just one of many of components of the adult gaming/entertainment industry.