Think about it: If His death only purged us of minor stuff like stealing crisps from a sibling as a child then it really wouldn't have been worth the effort on his part.
A simple "sorry" should be sufficient to cover petty sins like that; a human sacrifice would be, quite literally, overkill.
But if we all go round sinning our pants off then eventually the cost / benefit graph will move into the section marked WIN and His sacrifice will rightly be seen as having been a noble gesture to save us from our wicked ways.
Hmmm. This dilemma needs more beard stroking!