You seem to disregard the fact that what is being talked about here is getting involved with them romantically, intimately and inviting them into your life to stay, and then "helping them", which certainly does not work ever and is in and of itself a disorder, since what these people want is a state of perpetual misery with one another with the justification of "wanting to help" the other person, but which ultimately leads to just more misery.
Co-dependency, get it?
Relationships don't have a hard and fast rules. What applies to others may not necessarily apply to some. Not always. But i do get your point.
Co-dependency-based relationships aren't relationships, and the whole point is that you're NOT helping them, but simply feeding their emotionally destructive addictions. I'm not talking about healthy relationships. Did you miss the title of this post? This is co-dependency, which only serves as a destructive means of giving an addict more of the same drug that prevents them from solving the real issue, which will never be solved if people continue entering into romantic relationships with these people, because your emotional presence is their drug. That's the thing. "Helping" a person like that by giving them the drug is the opposite of helping them, which is why I posed the questions which gives people who feel like they need to help a set of ideas which might make them question their own desire of helping such unhealthy, codependent individuals, because if you try to "help" co-dependents by giving them a "relationship", which is exactly what they want so that they can feed off of your altruism, it always ends in disaster, 100% of the time.