The only "true form" of a given religion is the form held by the person claiming it to be true. Ironically, a terrorist also thinks they practice the "true form". So it's a meaningless distinction.

You're right, religion can motivate a full range of beneficial and harmful behaviors, and furthermore, there's no evidence it's a net win for society that people base their conduct on religious ideation. It's just confirmation bias to claim that a person's goodness is explicable entirely because their motivations are religiously framed. In my view, most people mean well and try their best to do well, often in spite of their religion.