One could argue for responsibility for one's actions in multiple ways.
The easiest would be to say we intuitively assign responsibility to our own and other's actions, which can be seen from our pride, praise, contempt, etc. for actions. Therefore, since moral responsibility is intuitive or self-evident, the burden of proof is on the opposition.
But, of course, there are reasons to support moral responsibility.
Maybe the pragmatic one comes to mind first. That is, our society would hardly function without responsibility and subsequent reward or punishment.
However, the crux of the matter is your implication of determinism.
And determinism isn't such a sound theory since its correctness cannot be knowable (you could also say it's self-refuting), or of anything for that matter, assuming it is true (If determinism is true, you are predetermined to believe everything you believe).
When you assume free will, you immediately assume responsibility for everything you do. And if someone brings himself into an unsound state of mind, he is responsible for that too.