Individuals have an inner thermostat, which makes us uncomfortable whenever there's too much or too little risk in our lives. People will speed on the highways... but only until the danger of this behavior hits their thermostat's set point. When laws are passed requiring drivers to wear seat belts, some drivers will find that the speed they'd been driving no longer feels right; it's not quite risky enough. So they'll drive a little faster till they again reach the set point.
Europeans who came to America in centuries past tended to be those with higher risk-appetites. Once in the New World, the people who moved further and further West were those with the highest need for and tolerance of risk. It's no coincidence that poker is considered a game quintessentially suited to America, and particularly to the American West.
Casino gambling in general is a way to satisfy risk-appetite in a meticulous way. On-line poker rooms offer games where the betting starts at one cent, and other games with bets of $1000 or more. Compare that to ordinary-life behaviors that involve risk (mainlining heroin, having children, etc), which are often all-or-nothing choices. Gambling is a way to calibrate more precisely the level of risk that fills our inner need.
When people tell me that they don't gamble, I sometimes reply that getting out of bed in the morning is a gamble. As is staying in bed. We don't have the option of avoiding risk, but we can manage the type of risks we do take.
The McManus article ends by quoting Mark Twain. "There are few things that are so unpardonably neglected in our country as poker. Why, I have known clergymen, good men, kind-hearted, liberal, sincere, and all that, who did not know the meaning of a ‘flush.’ It is enough to make one ashamed of one’s species."
