Okay, so it sounds like part of what you are saying here is that someone's act can only be evil if they were able to do otherwise than they did in fact do. You don't believe Hitler could have acted otherwise, therefore you wouldn't call him evil. — Leontiskos

Yes to your second interpretation, but "can only be evil if they were able to do otherwise than they did in fact do" is how i perceive the more common perceptions of good/evil, i'm sure my interpretation is both true and false in that regard...

This is because but-for causation casts a wide net. We would not want to conclude that knives are evil from the claim, "But for the knife, he would not have murdered." Nevertheless, what I think your argument does demonstrate is that thoughts constitute an important causal aspect of acts. — Leontiskos

The seem to constitute the origin of acts. As I laid out, plenty of horrid acts are not motivated by something bad. But some decent acts are. We can't quite make that work unless the thought it was made the act wrong by virtue of its intention. I don't know how strongly I want to argue this, but that seems the case to me.

1) why is it good when you convince someone to agree with you — Leontiskos

It makes me feel good (emotivism). Again, hard to explain that - but I think this answers the question you're asking. The 'why' is kind of a private, for-me thing to figure out and that's the semantic system I alluded to earlier.

2) why would you try to get other people to assent to your reasoning if moral issues are not susceptible to rational assent? — Leontiskos

To feel better.

If you don't think moral positions are susceptible to rational inquiry, then I don't understand why you would try to rationally persuade another person to adopt your own moral position. — Leontiskos

This is what I was getting at earlier - I don't. I try to get them to understand my reasoning. They might still morally disagree, but accept that, perhaps their act is likely to land them in prison, and so resile. That would be a result for me. Sometimes its fun to try to put the moral argument ot people, but its make me personally uncomfortable as I don't feel I have the right. These discussions are where I get most of my 'talk' out in the moral realm. It should also be clear that I only ever try to get people to either act or not act. I don't care much what their moral position is. I just either want A to happen, or A to not happen. I want them to do that. Not accept why I'm uncomfortable as their reason to do so (well, sometimes that's the case - my wife often does or doesn't do things for my comfort and vice verse but we share morality in that way so sort of moot).