Joseph Epstein's book snobbery contains a discussion of moral snobbery in which he offers the following anecdote:I like the emphasized sentiment immensely.
"I once found myself in a mild political disagreement with a middle-aged physician. I cannot now recall the matter we argued about, but when it became apparent that, as in most political arguments, no winner was going to emerge, he said with a complacent smile, 'Oh, you may be right, but all I know is that I care deeply about people.'"
It's perfectly true that it's not enough to have good intentions; one has to care about the effectiveness of one's actions at bringing about the intended goal. But it's also true that people who only care about their good intentions doesn't even have good intentions. If they really intended to, say, reduce poverty they would show some signs of wanting to know the most effective way to do that.
Which makes for a punchier aphorism?
If all you have is good intentions, your intentions aren't that good.or
If all you have is good intentions, you don't even have those.