Does the definition really matter? As soon as we deviate from "what provides the most net-positive objective benefit for me" to... anything, we're talking about what is and isn't "good for the soul."
You can argue that IF I get caught doing something bad I go to prison or face penalties, but that's a big if. If I can knock up married women and skip town, spread HIV (and with all the sex partners those sluts have, how will they know they got it from me?), get girls drunk at parties and nail them and nobody knows who fucked who, and so on, each of these actions is a net positive for me: I'm getting laid. Steal shit when nobody's looking, I'm getting richer. If I'm careful I don't get caught.
The moment you move from why society has rules to why I, personally, should follow the rules if I can get away with breaking them, we're discussing something not scientific. Scientifically, I should be violating the rules every chance I get if there's a profit in it. Liars and deviants gain larger and more dynamic and influential social groups. Drug addicts and dealers and serial rapists face consequences; the guy who gets your wife drunk and fucks her in the bathroom at the bar and knocks her up and she can't remember you and nobody saw it... he's in the clear, she probably won't tell you, and fuck yeah doesn't matter had sex!
People keep saying getting Jesus back in schools would be good for this country, versus how bibles don't belong in schools. Zen Buddhism would make a nice middle ground, if you could tell the difference between philosophy and religion--or even between "shall make no law respecting the establishment of religion, or prohibiting the free exercise thereof" and "Politicians have endorsed religion and the local school district has distributed bibles". (If congress shall make no law... how have we managed to ban religious displays in federal court houses, when Congress only makes legislation and the Court only judges action to be taken in favor of legislation, with the Executive Branch left to write policy and create government functions necessary to execute that which is prescribed by enacted legislation?)
And there's your spirituality: A book that says it's good for the nature of your being to... not be a complete fucktwit asshole. What do you mean, "the nature of my being"? Getting laid versus not getting laid IS the nature of my physical, biological, scientific being, isn't it?