I would say an Evil person who knows he is evil and does BAD things is WAAAAAY worse than someone who does not know what he does is evil.

That depends on the situation. At least it's possible to reason with such a person.

Wanting to have the power to do what you want for your own desires (in the Jedi philosophy there's nothing wrong with death) is not a "good cause."

It's certainly a "good cause" if one puts it as "the power to save the ones you love". The fact that it transformed to a desire to do ANYTHING you want is another matter.

I remember when I was 7, that is even before knowing about Star Wars, I (after one rather unpleasant moment in my life) was sitting in my room thinking about a lot of things. One of them was - what makes me a bad person? I had a lot of questions, some of them on the if killing will make me a bad person topic. What if I'll kill to protect my family? I know the one I killed could have had a family too, you know. And so on and so on... Yeah, in my childhood I thought about things that I don't think any sane kid would.

"A tool to kill Vader" is not at all how I see it. In fact, didn't Yoda try to encourage Luke not to rush off and fight Vader? And if they both thought that Vader was unsavable (as did Palpy and Vader himself) it doesn't mean they wanted him dead... only that they didn't see an alternative.

The only problem is, all that doesn't make Luke less a tool. The reason Yoda tried to encourage Luke NOT to rush off is because he wasn't ready to, well, kill Vader.

And, about lying, there are many ways to lie to a person. Obi-Wan could lie about Luke's father a lot of ways. But he specifically said that it is Darth Vader who killed Luke's father, placing the desire for revenge (not the Jediest way to do at all) which would actually help their goal - kill Vader.