Anyone believing that no individual can have an effect on society's future will as a result feel too helpless to act to change society for the better.
Conclusion (Thus)
Anyone who wants to improve society should reject the belief that its future will be determined entirely by vast historical forces that individuals are powerless to change.
rephrase: if you believe that the future will be controlled by things you're powerless to change, this will not improve society.
Evidence
If you believe that future is beyond your control, you will feel to helpless to act to change society for the better.
Evaluate
Consider this similar argument: Anyone who compliments Obama gets approval from Lisa's Dad. Thus, if you want Lisa to like you, you should not compliment Obama.
This is missing the idea
The argument we read had the same form. Anyone who believes "the future is out of our control" will feel too helpless to act. Thus, if you want to improve society, don't believe that "the future is out of our control".
So we'd be missing the idea,
Goal
Look for some answer stressing that .