Now, in the Buddhist sense, a sutra is a story, with some argument that the word literally means “gospel”, “good news”. They in general are recollections of some explanation of a topic by the Buddha while he was teaching, and so they start with the phrase “Evam maya srutam” — “This is what I heard”.
So this is what I heard, in abbreviated form. The Buddha visited a group called the Kalamas, and they, after making properly respectful gestures and noises, sat down and asked the Buddha, “Look, we get lots of holy men through here. They tell us lots of things, and some of them are pretty goofy. How are we supposed to tell the good ones from the bad ones?”
Buddha answered, “You’re right to be uncertain. So, don’t believe something just because you’ve heard it stated repeatedly; don’t depend on tradition; don’t depend on rumors, or what’s in a scripture; don’t depend on guesswork; don’t depend on something because you take it as an assumption; don’t depend on some argument for which the logic doesn’t stand up, or something that you’ve just thought about for a long time, or because someone smart is telling you, or even because your teacher said so. When you yourselves see something is unskillful, leads to greater suffering, then stop doing it.”
The lesson goes on a bit, not too much but Buddha’s audience couldn’t click over to cat pictures. Buddha does, though, repeat this same teaching in positive form: “When you yourselves see something is skillful, leads to reducing suffering, then do it.”
Bodhipaksa’s objection to the controversial translation is in the part about “if it doesn’t agree with your own reason and common sense”. After all, there’s a lot of Buddhism that doesn’t agree with common sense in some ways, like the notion that we don’t have a permanent soul or identity — I mean, golly, it sure seems like I do! But what Buddha is really saying in the Kalama Sutra is common sense: if you don’t want a life filled with unsatisfactory unpleasant annoying and generally uncomfortable feelings, suffering, don’t do things that increase suffering, and do things that decrease suffering.
Basically, what the Buddha is saying in the Kalama Sutra is that Buddhism is an experimental science: you shouldn’t just trust what someone says. Test it against the real world: do you suffer more, and do others suffer more, because you do something? Then it’s unskillful: don’t do it. But doing skillful things reduces suffering, yours and others, so do them.
It’s really that simple.