The common sense would tell us that stealing is illegal. It does not matter what somebody steals.
What if someone steals your 'idea' - is that illegal according to your dumb analysis. What about 'time', what if someone steals your time? is that illegal? According to your rule, it is. But according to the real law time is not tangible so stealing someone's time is not illegal.
Bitcoin is also intangible. Therefore, you can steal it all day long and you are just manipulating bit patterns on a crazy continuous list of similar bit patterns. It is not illegal to put some bit patterns on the blockchain. If that has the effect of 'stealing bitcoin' - it is just tough shit for the guy who lost them - but it is not illegal.