weak-minded

Stupid, she told herself. Vain, weak-minded, and stupid.

Plato sympathizes with the desire to influence weak-minded people. However, rather than directly controlling the minds of such people by the power of his own will, he uses the power of his thought to construct a myth designed to control the beliefs of the weak-minded by appealing to their imagination.

I have lost count of how many timesI have heard that Christianity is a crutch for weak-minded people, who can't make it in life without faith.

Altogether thirty-four out of 146 'criminal lunatics' admitted to the asylum between 1852 and 1890 were described as weak-minded or imbecile by the asylum staff.