Why do some refer to the United Nations as a club where they plan against the weaker nations ?

Answer 1

The U.N. is a useless entity. It is internally corrupt and uses it's power to benefit it's members. They make hollow threats to countries and never back their own decisions.

Answer 2

Many of us consider the U.N. as a club where those who do not contribute plan to get more money from those who do; often as loans which don't have to be repaid.
When rulers from "broken toilet" countries retire with wealth, they tell their subjects it's all the fault of the richer countries. Go figure.