Adding in- as a prefix in English turns out to be more complex than it at first seems. All you have to know is the meaning of in- and the origin of the word.
negation
If you were looking for a ‘good’ night out with a ‘bad’ man or woman, would you prefer someone who was amoral, immoral, or non-moral? Here comes a strange trip into English morphology…
The Eclectic Light Company 