dear MrFreeze...
you said:" I would say that those who are mentally disadvantaged are more prone to having their minds molded by other people. Is it really them believing in God or is it the influence around them?"...my answer would be: depending on the individual and their handicap they can be trusting a caregiver and honestly believeing in God or they can be ones that aren't held responsible for their choices or actions at all because of a significant barrier to "emotional" freedom.
the bible says and I believe and have said recently that God would be merciful to people like that...based on His standard, which is Truth. ie. if you have never heard about God and you are an evil person...you would be judged on the evil you do/think.(you are a law unto yourself)
having Jesus Christ as your Saviour doesn't preclude you from judgement AT ALL...all believers will stand before the judgement seat(2 cor 5:10) knowing this we are admonished and helped to present ourselves acceptable to a Holy God.(romans 12:1-2)
love michelle