I think in the subtext there is a criticism with MWD, but, that's my reding of it...
Penny has, on her forums written that she has a lot of disagreements with MWD on the subject of infidelity. Within building a healthy and lasting marriage she raves about MWD, but PT has a much more aggressive stance on infidelity and is 100% in line with it being an addiction.
That's a big part of the original debate in the other thread, what is more effective in combatting infidelity - bcoming the perfect partner or playing hardball?
And yes, you like many people (including myself) who read MWD try the softball approach and end up frustrated or in some cases (mine) physically ill.
I wasted a lot of time using Bo-Peep until I was so ill i went to a doctor. And I NEVER see a doctor, I despise them.
The resentment does build up yes... PT comments on this too, the protection phase isn't just for you, its for your spouse and for your marriage.. in her view having regular exposure during an affair erodes YOUR respect for yourself, your spouse, and your hope for your marriage.
Further your spouse is exposed to that negative energy and watches your hope fade and it just makes things worse for them too.. they can FEEL the resentment building... protecting your spouse from that gives them a more positive view of you.
In a way, it might be best to do Bo-Peep long enough to leave your spouse with a good last impression and then to go into protection phase... rather than going in there looking like a miserable hag so to speak.. which can happen.