It looks as if the way to solve Ordinary Jo’s problem is to make thoughts about right and wrong more like desires: that way they can conflict, or get in each other’s way. Here’s a famous way of doing that
Thinking something is right is a bit like wanting it to be done (at least, you can’t really think something is right without wanting it to be done), and thinking something is wrong is a bit like wanting it not to be done (at least, you can’t really think something is wrong without wanting it not to be done).
What kind of conflict between moral thoughts and desires does moral internalism give you? That depends what you think about desires. Suppose you accept moral internalism and also believe what Ordinary Jo believes about desires. What do you get? Something similar to David Hume’s view:
This is the Humean view of akrasia: Firstly, you can’t really know that something is right and not do it, or know that something is wrong and do it anyway – because you can’t really know anything about right and wrong. Secondly, if you think something is right and don’t do it, or think something is wrong and do it anyway, you will have to have wants pulling you in different directions in the same time
Does the Humean think akrasia is irrational? Not really: the Humean just thinks that moral beliefs and desires compete for the same space. Is that enough to make sense of the feeling that there’s something specially bad about not doing what you know is right, or doing what you know is wrong? Perhaps the idea is that there is something specially bad about being in the kind of psychological disorder which is involved when you have different desires competing for the same space.