Correct answer: taxes ensure that citizens contribute to meeting society's needs.
Yes, politicians get paid through taxes too, but that's not the reason for taxes. Government leaders are working on behalf of society and seeing that societal needs are met, so paying their salaries is part of the need that society is supporting through taxation. And we don't enact a government program immediately for "every need that arises." Citizens and legislatures and leaders work together to decide what programs are needed in society and what will get funding -- from defense to roads and infrastructure to social programs, etc. And tax money does not go to private businesses - unless they are receiving a government grant for some purpose that serves a community need. Private businesses fund themselves, and indeed pay taxes to the government.