A person is inherently good or bad.
That's rubbish. a) People are a lot more complicated than that and b) 'good' and 'bad' are subjective terms. One man's freedom fighter is another man's terrorist.
That's not the point. The point is religion doesn't make you a bad person unless you were already ready to do bad things to begin with. It's just another reason that you use to justify your actions. If you're ready to kill someone "in the name of God", then you would be ready to kill someone without that religion as well.
You describe the outside point of view on that person. If someone kills infidels in the name of God, he is a hero and martyr for one group of people, and a monster for the other group of people. That doesn't affect the main point, that he's ready to kill someone for some