"Assume Good Faith" is one of the fundamental principles of Wikipedia. In general, it works for them because most people are indeed trying to help the project, not hurt it. Can we apply that principle to onboarding? I vote yes.
In general, most try to help a new team member, not hurt him or her. The organization likely invested time and effort to find, select and convince that new team member to join in. The organization as a whole believes that new team member can strengthen the collective. Thus, it is in the organization's best interest for that new team member to succees.
Don't Follow Your Principles Off A Cliff
But, and it's a big but, "in general" is not the same as always. There are going to be people that act in bad faith. There are going to be people that feel threatened by a new employee and try to hurt him or her. So, just as Wikipedia counsels not to follow the assume good faith principle too aggressively, the same is true in onboarding. Assume good faith as long as you can, but always be ready to deal with people acting in bad faith.
