It doesn't mean that people with good intentions don’t have bad ideas. They often do. And it doesn't mean that people with good intentions don’t do stupid and even bad things. They most certainly do. But, giving people the benefit of the doubt means that we start with the assumption that very few people wish to do us harm, that very few people purposely want to do bad.
We should always start a conversation or a relationship with the element of trust until shown otherwise. I know it is risky but I also know that it is rewarding. When you start with trust you are usually reciprocated with trust. There are exceptions to be sure. But we shouldn't allow the actions of a few determine how we see the majority.