@Clint_L I think you provided the OP the answer he was looking for.
In the given setup of the thought experiment, there was an apparent difficulty in "how could one be sometime fighting Good" by being a Muscular Neutral who tries to ENFORCE neutrality, or "how can one not enforce Good and not be a jerk at the same time".
I think it's because Good as defined in the OP can't win against Evil because... they can't fight it.
We're told that "Good is altruism, respect for life, and a concern for dignity of sentient beings" while "Evil is harming, oppressing and killing others". It is added that a victoy of Good can't be harmful for anyone and that there will be no brainwashing of people.
So, if I am evil, I go in a Good society, notice a jewelry and take that big fat ruby (that can or cannot help me cast a spell needing a ruby worth 500gp since I got it for free, but that was another thread sorry) and go away. What can Good do? I can't be harrmed or be imposed detrimental effect. So I am put in front of a good Judge who appeals to my altruism and let me free to go put back my ruby in the shop and apologize to the shopkeeper, offering to clean his windows as a gesture of repentenance. Yay me, I can sell the ruby and spend all the proceeds at the tavern! And I won't lie to the judge, I'll just tell him that I didn't made him in charge, so he can talk all he want, he is not my boss and property is theft anyway.
Neutral would oppress me and put me in jail instead, having no qualm in oppressing me to enforce their "property" silliness.
Evil would kill me and take my stuff, even if I hadn't stolen it.
In this setup, Neutral would oppose Evil (because they think the whole killing, harming and oppressing others is not something that should be done... unless one has a valid reason to do it) and they would oppose Good when Good would be on the verge of winning and starts saying things like "hey, we think altruism is so great that we will remove taxes, taxes hurt so many people, I am sure people would give enough money for the keeping the administration in a working state if we replaced the tax code by a charity box!" And then Neutral bash their head with a giant club, tell them "you're not fit for running a government, go back to your monastery/philosophy club and let the reasonable people be in charge..."