Doing bad things ("evildoing" if we want to express it in a morally absolutist way) is generally not for the pleasure of it, but it's simply doing what's good for oneself with little or no limits (if one can get away with it) on how bad the consequences for others are of one's personal upside maximization actions.

Whilst "malice" is per the dictionary a specific kind of doing bad things were one actually wants to harm or hurt others, hence that saying with that word specifically can't be easilly turned around (especially as actual malice is pretty rare), if you use "calous selfishness" instead the reverse saying ("don't attribute to stupidity what can be explained by calous selfishness") is often true, especially when it comes to people intelligent enough to be able to figure out the broader consequences of their actions.