They want to achieve something for the greater good, or at least for the good of someone else.
They have a selfish goal that harms others, such as gaining ultimate power.
They have principles about what they will or will not do to achieve their goals. For example, they may refuse to harm innocents.
They do not care who gets hurt or what damage is done in pursuit of their goals.
We understand why they are behaving this way, and perhaps even agree that their motivation is valid.
We do not understand their motivation, or we find it unsound.
We have seen them suffering and experiencing trauma, and felt sympathy or empathy for them.
We have seen nothing to make us empathise with them.
There are aspects of them for which they are likeable—for example, they may be funny or kind to animals.
They have no likeable qualities.