if you do the utilitarian math, robbing banks and giving them to charity is still a good deal

Only if you're bad at math. Banks aren't just piggybanks to smash, they perform a useful function in the economy, and to disrupt it has consequences.

Of course I prefer to defeat bad utilitarian math with better utilitarian math rather than with ethical injunctions. But hey, that's the woe of bounded reason, even without going into the whole corrupted hardware problem: your model is only so good, and heuristics that serve as warning signals have their place.