What is the meaning of Thoreau's quote "There is no odor so bad as that which arises from goodness tainted"?I simply dont get the meaning of this...

In this passage, from the first chapter of "Walden," Thoreau is talking about how bad it is when people try to *do* good (especially for others).  Instead of trying to *do* good, we should try to *be* good -- the best we ourselves can be, and never mind worrying about whether that helps others.  If we do that, it will actually turn out to be better than if we consciously try to *do* good.

If you look a bit before that, he talks about how the sun does best when it ignores everything else but just shining as brightly as it possibly can.  Compared with that, when Phaeton tried to do good for others, he burned a bunch of stuff up.

So Thoreau is saying that people who try to *do* good for others stink (figuratively) and that they'd be of more help if they just tried to be good to the best of their ability.

In a way, this is like the capitalist defense of self-interest that argues that when people act selfishly (trying to get the most possible money for themselves) they actually end up helping society.