That's a good question. Do we idealize everyone? If no, then there must be a reason why we idealize those we do. I don't think it is choice though. I think it is subconscious. I suspect we idealize those we fear, for example; when we idealize the person, we make them not threatening because our magical thinking says they are safe (based on our idealizing, which is not based on reality).

It's a good question and deserves much thought.