This is an essay, a page containing the advice or opinions of one or more Wikipedia contributors. Essays may represent widespread norms or minority viewpoints, and they may be heeded or not based upon your judgement and discretion.
There are many good reasons to be involved in Wikipedia:
It is a self-governing mechanism that creates positive externalities
It's fun.
It's educational.
It's social.
You are part of an exciting development making use of the open source idea.
You can correct other people on the spot without asking their permission!
It's interesting to share your knowledge with other people, particularly knowing that others can instantly edit or react to what you've written.
To contribute is to gain.
Did we mention, it's fun?
Ultimately it's yours.
Most likely their kids will use it. (You get the point. It's like you own a 1,000 volume encyclopedia at instant access.)
It gives you something to do. (You can probably do it at school/work as well as at home since it remains unblocked at many schools and places of work.)
Learning to write in a neutral point of view is a useful intellectual exercise, since it requires cultivating humility and respect for the views of others.
Wikipedia is a remarkable phenomenon of social organization; learning how things work here provides valuable lessons for many other kinds of organizations.