RE,
1. There is a machloket regarding deriving benefit from mitzvot. Rashi says that they are a yoke. Rashba says that the benefit is in the next world and this is not considered a prohibited enjoyment (e.g. in the case of a neder). Rand was an atheist but she might agree that even a perceived benefit negates it being altruism as the person feels good about what will come to him.
2. The Malbim says that it is an atonement for them. That is why the word used is חטאת and not חטא.