Act 1.7 of Shakespeare's Macbeth is before Duncan is murdered. Technically, the soliloquy doesn't prove anything, since it is before the assassination. At the same time, of course Macbeth is responsible for Duncan's murder--he does it. Thus, a suggestion isn't needed and is superfluous, or extra. Macbeth kills Duncan and is guilty of murder. I'm not completely sure what you are "stuck" on, or what angle you're coming from.
This soliloquy reveals the doubts or second thoughts Macbeth is having. He would be more willing to go through with it, if not for the possible consequences: on earth and in the afterlife. He feels badly because Duncan has been a humble and fair king, and has treated Macbeth well. And he is in the process of performing the role of Duncan's host, and by rights should be protecting Duncan from murderers, not murdering him himself.
Macbeth has a decision to make. He will make it soon enough, and although he is berated and manipulated into deciding to go ahead with the assassination by his wife, he still makes the decision. No person or outside force makes him kill Duncan. He decides to do it and he does it. He is responsible for killing Duncan. This soliloquy demonstrates some of the issues involved, and thereby does suggest Macbeth is responsible: it shows him thinking the act over. It shows him in the process of making the decision. But the proof of his responsibility is in the act itself.
I will just add a crucial point of self-consciousness to the answer already posted here. The soliloquy in question is not only important because it helps us to put the blame or the responsibility of Duncan's murder on Macbeth. It is more important to note that Macbeth, in this speech admits this responsibility himself. His course of thought is a profoundly philosophical and metaphysical course of moral thought. This is what distinguishes him from another run of the mill murderer.
Throughout the speech, he meditates on divine justice and concludes that there is judgement here inevitably on this bank and shoal of time where his finite life is housed. He knows that the murder cannot hush up its moral consequences and the nemesis will hit back at him. He tries in vain, throughout this speech, to ethically justify to himself, this act of his. But as it appears to him, it is unethical in all possible ways--in terms of both kinship and hospitality.
I mean Act one scene SEVEN. Typo :/