I'm reminded of Ramana Maharshi's simile that compares nondual awareness practice, seeing consciousness or awareness as if it were a self (as in, the opposite of anatta), as "the stick that stirs the fire and is consumed by it" because eventually awareness sees through the self-illusion. I wonder if in the same way, the ego cultivating metta would eventually be overwhelmed and consumed by the metta.
At any rate, the ego's job, according to western psychology, is to create and maintain healthy mindstates and prevent and dispel unhealthy mindstates. If your choice is between cultivating metta (with ego) and not cultivating metta (with ego), then the choice seems obvious. If there's going to be a sense of self, it may as well be a sense of self that produces beneficial results. The self-illusion isn't completely seen through until arahatship anyway, isn't it?
