Well, let's dissect the Sadistic Conclusion. Basically, it is a specific variant of another, broader conclusion, which can be stated thusly:
If it the addition of a person or persons with positive welfare can sometimes be bad, then it is sometimes preferable to do other bad things than to add that person or persons.
Wait what? That's the direct opposite of the Sadistic Conclusion. If the Sadistic Conclusion was commonly accepted, then people would abstain from using contraception if they thought that they could create new suffering-filled lives that way. And if they thought their kids were about to live happy lives, they might try to arrange it so that the kids would live miserable lives instead.
That's not the Sadistic Conclusion as presented by Arrhenius. Arrhenius' Sadistic Conclusion is that, if it is bad to add more people with positive welfare, then it might be less bad to add someone with negative welfare instead of a large amount of people with positive welfare. Obviously the amount of people with negative welfare must be considerably smaller than the amount of people with positive welfare in order for the math to check out.
Under Arrhenius' Sadistic Conclusion adding unhappy, miserable lives is still a very bad thing. It makes the world ...
Joshua Greene manages to squeeze his ideas about 'point and shoot morality vs. manual mode morality' into just 10 minutes. For those unfamiliar, his work is a neuroscientific approach to recommending that we shut up and multiply.
Greene's 10-minute video lecture.