Would extraterrestrial beings be likely to believe in capitalism?

It is possible they believe in capitalism but wouldn't see us as worth having anything to trade with.

They'd still have to cope with economics, the allocation of energy, talent and resources. For example, they may have much more advanced technology but don't have unlimited resources to decide how many ships to build and which projects to build on what schedule because you cannot do it all much less at once.

How to answer the questions related to science & our future in a debate confidently

Read newspapers and take few articles / topics and start competing on the same with your parents or friends and try to win those.If you are failing at any point of time , you will come to know where you are doing more mistakes or ask them where they are stronger than you.

Why are so many people so unwilling to believe that evil exists?

Well the thing about the concept of evil is that it is very subjective.Two-hundred years ago slavery was widely accepted. Some African tribes today still practice infantcide. There are so many other examples of different times and places where things we consider evil today were not so evil then.Ethical values vary from culture to culture and time period