Everybody has their own 'truth', there is no 'absolute truth', so any judgement is flawed from the start. There is something that comes up in all debates, and that is extreme cases and/or exceptions to the general rule, which reflects that lack of absolute truth.
You're right (in my opinion at least, though you need to read some metaphysics), but I don't think you're drawing the right conclusion. If truth is subjective, then that means that whatever I believe is true is true, and whatever you believe is true is true, even if the two conflict. But, what if all your life you was taught that life is suffering, and therefore you should kill everybody to free them of that suffering? That would mean that it is true that you are morally obligated to kill everybody.
In fact, by your arguement, anything can be either moral or immoral. It can be moral for me to beat you up. It can be moral for me to steal. It can even be more for me to manipulate people for my own personal gain, knowing that it will hurt them.
When you say that truth is subjective, and therefore so is morality, that doesn't mean that you can ignore extreme situations, it means that anythig can be moral or immoral. You still have to justify extreme cases within your own moral system.
I don't think that lying is evil in itelf, as not all can deal with the truth. Lets say a doctor knows his patient has a fatal illness, but informing the patient of this would cause great distress and serve no constructive purpose, whereas a lie would allow the patient a few years of quality life. Is the doctor wrong in holding the truth? Wouldn't it be cruel, thus evil, to tell the truth to his patient?
Not an easy situation, right? Both sides could be argued here, but IMO all these situations have no universal resolution, and what is right for one person has to be determined specifically.
If your personal moral system says that you're obligated not to lie, you're still obligated not to lie. It's still immoral. It's just that, in your personal moral system, you also feel obligated not to cause somebody emotional distress, so that would also be immoral. The question is which is more immoral.
I would describe an evil individual as one who takes pleasure in, or is unmoved by the suffering of others, and activelly seeks to create conditions creating or maintaining that state of suffering. I guess that could be called 'extreme egocentrism', as what we usually consider as 'good' are values like generosity and emphaty.
That's an evil person in your own personal moral system. My personal system may say that an evil person is somebody who tries to imperialistically impose their beliefs (like their belief about what makes a person evil) on others. Or, I may believe that nobody is evil, because morality is subjective.
Edit: Sorry, I can't figure oiut what's wrong with the BBCode, if a mod can fix it, that'd be greatly appreciated.
As for this Hitler arguement: No, Hitler wasn't evil or immoral. He might have been by your personal system, but he wasn't by the system of lots of other people, or by his own personal system.
But, we were justified in attacking him, because that couldn't be immoral either.