In an atheistic viewpoint, using contraceptives is basically a bug. Look at the real motivations; it's so you can have sex (satisfy reproductive drive) but not have the burden of actually reproducing, so you can still be comfortable. One way or another, it boils down to that. The drive for comfort (or laziness, depending on how cynical you are) is, I assume, another survival instinct to encourage conservation of energy for when it's needed.

Basically, if you don't have an immaterial soul, all your actions are determined by evolution. It's just a question of how optimal your evolutionary programming is. Almost no one really believes this and persists in believing that there is such a thing as moral behavior, which really ought to be a clue.