Being malleable is key to success in magic, and if one is not aware of the magic s/he is doing, then it is key to "life."
Morality is subjective. Consciousness and shared beliefs (i.e. egregores and god forms) create reality, and because of this, objective reality does exist, but not absolutely. A paradigm shift will result in operating under a set of conditions and rules with potential to be a totally inverted reality when contrasted against the previous. Nihilism is a stepping stone to truly comprehending (not totally, but truly) what is going on and why it happens. Nothing exists, everything is permitted, do what thou wilt.
That being said, your question is asking about the functionality of a specific paradigm. If you do not see the potential for gain in being "moral," you are CHOOSING to be blind. Doing good has a ripple effect in reality, and it seems to defy enthalpy. Instead of losing energy when dispersed throughout the system, putting in love multiplies at an exponential rate. Give 5 units of love to person X will really end up with X putting out, say, 5.5 units of energy to the system. This ripples throughout the system and it eventually comes back to you. Conversely, stealing a TV from X will piss him off, and perhaps prompt him to steal from his employer who then lays off employees. This too will eventually come back to, perhaps indirectly. Also keep in mind that the links closest to the initial drop of the pebble into water will experience the most intense gain, even though the ripples grow as they get farther away from the origin. That is why YOU notice your actions impacting your life. Karma is a very useful paradigm. It makes you feel good when you do the "right thing" too, which is a plus.
Of course, there may be times when morality gets in the way of the end result. At these times you will either need to develop a system of justification for your actions to keep operating under karma without negative consequences or adopt a more nihilistic philosophy to get shit done. After all, what matters are results.
I hope this tells you why you should or would want to be "moral."