Which illusion is the ultimate weapon ?

1. Immortality

2. Religion.

Note that atheism is no solution too.

But think about agnosticism.

It frees from taught and cultural errors, misjudgements and hallucinations.

There are forces that are stronger and more intelligent than the human species (For example earthquakes, vulcano eruptions, black holes and art that inspires the imagination of people in such way that these are doing things they wouldn't have done without).
Do what you like be the whole law. Love is the law, love at will.

By the way: Many people have enough time and resources to spend their energy and creativity for different things than destroying the things they and others need for life.
Since the end of the big ideas like idealism, communism and individualism the most important criteria for acting is if the target of somebodys behaviour is fructuos.
Because ethics and aesthetic are transcendental it is sometimes more or less difficult to judge if somebodys actions are more good or more bad. What is bad for someone, might be good for others and relativity cannot be the criteria for dealing with actions of others (-> "Categorical imperative").
That doesn't mean that you don't need laws (Hopefully not created by your secret enemy ;>) ).
People who overestimate their own freedom higher than the right of others to live in peace and their own standards must be controlled or
stopped.
People construct machines that are able to do things, their creators cannot acheive. Since humans are the god creating species or at least a species that create the idea of absolute beings that are superior to everything and everybody else, this idea competes with new developments of microtechnology, bionic, genetics and computer science. May be it will be better not to implement the idea of god into machines. But why care for themes that will emerge only in the far future ?

3. Unfortunately: World wide peace