Bitcoin is a money and stealing a money is absolutely illegal actually stealing anything is illegal and bitcoin has a good nice value to how it can be legal.
yes in every society and in almost every religion stealing is a sin and not morally good. so i can say that stealing of bitcoin is a sin and illegal as stealing of money from some one. so we should avoid every type of stealing.
That is true why you think that stealing bitcoin if you can earn with bitcoin easily. We know the value of bitcoin is huge as of now but this is not the basis to steal bitcoin to others that is really bad idea.