It is a continuum, not binary. We all compartmentalize to some extent. When I come home from work I rarely think about work. I don't socialize much outside of work with my coworkers, and when I do I really don't want to talk about work. Golf league is golf, so let's not discuss crap from work even if we are coworkers.
I think in fact it very much is what the typical cheater does. They are living two lives. Now of course there are all kinds of affairs and cheaters, so we can find exceptions to everything. But the typical affair involves setting up separate orbits which do not intersect with the only common point being the cheater.
Those out towards the extreme who are pathologically personality disordered are un-safe partners. I agree with you on that. For some people this is one of the biggest shocks of discovering an affair, when they also discover just how disordered their spouse really is. These people are a small minority of the population and would be the sociopaths etc.
I don't think it is as binary as you portray, with cheaters being simply ****ty people who don't compartmentalize. There are many who know what they are doing is wrong but they believe they can control their two galaxies and that their spouse will never be harmed. They do rationalize their behavior as ok based on the separate galaxies will never meet. They are both ****ty people and compartmentalizers.
Nope not buying it. I think you are giving them way too much moral credit and actively downplaying their conniving nature.
Typical example, man is cheating on his wife. He tells his wife he is going out with his friend when he is really meeting up with OP to have sex. In that action there is absolutely no compartmentalizing. He has to actively lie to his wife and then drive to the place, have sex and then continue to lie when he gets home. He has to make sure his lies match, and he always has his story straight. Every time he lies he is not separating these two worlds he is active in both of them, it just in one he chooses to lie. In fact he has to think about both of them just to make sure he doesn't get caught. This is why many cheaters talk about how glad they are it is over so they can stop lying. To lie like that you have to be intensely focused on both worlds.
What I described there is a typical scenario of a cheaters life. It is nothing like coming home and forgetting about work until the next day. Cheating is an action, not a mindset.
To me compartmentalizing as you describe it is an out so people don't have to deal with the hard facts of the nature of cheaters actions.
The truth about a successful cheater is that they have to actively lie in about almost every area of there life and mostly of the people who the claim to love and are with them almost every day. They have to live an inauthentic life. They may be able to shut down the shame, guilt even remorse but this is different the compartmentalizing. It is suppressing their feelings.
The act of cheating is way too complicated to be able to work the way you say. It has to be a part of your entire life to be successful. It involves way to much subterfuge, you have to activity work at it every day.