You can very easily lose your players. They can create a new account by using a different address or using the name of their spouse, sibling, etc. People do this all the time and if I was a regular player, I would create a new account to get rake back if I was not already getting it. Only losing players do not know about the rake. The winning players are very well aware of the rake and it is the winning players who generate a bulk of the profit. Losing players usually have no clue about a rake, but they do not generate that much in comparison to a winning player.
Also, I agree with you that the market is not saturated. My play and real money sign ups are hitting all time highs. I never called the sites unethical either. The sites can do what they want, but from an affiliate viewpoint, I think banning rake backs would be ideal.
Lets not fight about this, we both do not care for rake back programs.