Can bad motives cause "do-gooding" to be sin?

Anonymous asks in response to one of my earlier posts:

Anyway, I was curious about how "to do good without it being driven by love is sin." Do you mean that good deeds motivated by pride or a desire to be rewarded or in order to get ahead are a sin? What about good deeds out of a sense of obligation? Just curious.

My answer:
Because according to Scriptures motives are as important to God as the acts themselves. Or to say it another way, transformation from God is seen more in a radical change of motives than it is in just a change of actions.

1Corinthians 13:1 If I speak with the tongues of men and of angels, but do not have love, I have become a noisy gong or a clanging cymbal. 2 If I have the gift of prophecy, and know all mysteries and all knowledge; and if I have all faith, so as to remove mountains, but do not have love, I am nothing. 3 And if I give all my possessions to feed the poor, and if I surrender my body to be burned, but do not have love, it profits me nothing.

Matthew 6:1 "Beware of practicing your righteousness before men to be noticed by them; otherwise you have no reward with your Father who is in heaven. 2 "So when you give to the poor, do not sound a trumpet before you, as the hypocrites do in the synagogues and in the streets, so that they may be honored by men. Truly I say to you, they have their reward in full.

In Matthew 6, Jesus is exposing the Pharisees' hypocrisy and while he never calls their outward acts driven by self-centered motives "sin", he portrayal of them speaks even more strongly in that direction, as seen in

Matthew 23:25 "Woe to you, scribes and Pharisees, hypocrites! For you clean the outside of the cup and of the dish, but inside they are full of robbery and self-indulgence.
26 "You blind Pharisee, first clean the inside of the cup and of the dish, so that the outside of it may become clean also.
27 "Woe to you, scribes and Pharisees, hypocrites! For you are like whitewashed tombs which on the outside appear beautiful, but inside they are full of dead men's bones and all uncleanness.
28 "So you, too, outwardly appear righteous to men, but inwardly you are full of hypocrisy and lawlessness.

Romans 14:23 "whatever is not from faith is sin."

Cain's offering in Genesis 4 was not received by God why? We don't know for sure but it seems to flow from not being given of the first fruits (he gave leftovers; his heart was not fully behind the gift/act.)

Righteousness in the Biblical faith is more than what is done (though not less). It is rooted in a response to God leading to love for God and love for men. Anything less than that is sin.

Having said that, I don’t mean we shouldn’t do acts of kindness if we lack love. [When we are faced with a less than loving motive (only in glory will our motives be 100% pure) and the opportunity to show kindness, we should still show kindness.] I do mean that our lack of love exposes our sinful condition and should lead us to repentance before God, acknowledging that our non-love-driven “good deeds” are less than what pleases God and looking for Him to so transform us by His Spirit into Christ’s likeness that we would truly love.

Biblical Christianity is more about joyously pleasing God than it is about being good people. As a matter of fact, "do-gooding" often is aimed at distancing ourselves from real lived-out dependence on Christ’s intercession for us (which is the heart of the Christian Gospel), by trying to feel better about ourselves or offer God a sacrifice less than what He has already provided. To see more of what I am talking about read John Piper’s Desiring God [online at http://desiringgod.org/dg/id1.htm].