Exactly
That is what happen when you meet someone who actually cares how people write good stories
No, they precisely have to think according to their character. And right now, you are not reasonning based on their characterization but on how you THINK they should behave based on their status.
Imu is someone who makes gamble and who takes risks, I already pointed that out in another thread. His power is based on the notion of fear and complete control, as such he always act in the principle that he is above all. Not in an Enel way where he is trying to convince himself that he is a god foolishly by trying to control the population, no. Imu KNOWS that he is the god of this world and that this simple fact is just a natural consequence of what he thinks to be his fate.
In other words, like Luffy and at the exception of Joyboy, Imu has no fears. His outer shell is like Kaido's, impenetrable. He knows his strenght and his power and until a few hours ago, he though that he shouldn't even have to move to take action.
On top of that, he is a very despicable person and seems to believe that anyone below outside of his circle is worthless. So it's perfectly logical for him to use Xebec to kill his wife or to fight Garp and Roger. He will not attack himself, he prefers to let others do the job for him.