Akrasia is a simple concept to relate to as a human. I can think of times where my will has been weakened by a strong desire for something. The something can vary, whether for gluttonous reasons related to food and drink, or for physical pleasure, or anything in between. Clearly akrasia is intuitively related to the human experience.
With no weakness of will it seems again that our nice excuse showing that Leontius did not do wrong willingly is now gone. It is still possible however, that Leontius was not willing if instead of a weakness of will there was some sort of biological lack of choice at play.
This is where Strawson's argument that humans cannot be morally responsible comes into play  The argument runs that nothing can be the cause of itself, or causa sui, and only things that are the cause of themself can choose their own actions morally. As human beings are not causa sui, they therefore cannot be held morally responsible for their actions. In other terms, as human beings are the sum result of our genetic endowment, and our environmental upbringing, both of which are the source of all of our actions, we cannot be held morally responsible as humans have no choice in the formation of either their own genetic endowment or environmental upbringing.