If you do not agree, then fail to pay your income taxes, or try to grow and sell peanuts, or braid hair for money without a license. Interestingly, economic markets are most famous for the relatively rare and significant exceptions to the purely voluntary example noted above. While significant and more exciting, such problems are relatively rare. Moreover, the outcomes of the two market transactions are fundamentally different. Political markets merely move wealth around, transferring money from one party to another.
Economic markets create wealth since both parties benefit from the trade.
Likewise, economic activity is typically a positive-sum game. In the selfish pursuit of greater income, producers inadvertently benefit others. The widget manufacturer may strive to make a better and less expensive product because of his deep-seated love of humanity, but more likely, his primary goal is to earn a better living. But in political markets, self-interested agents have an incentive to develop even more sophisticated ways to take money from the general public. Furthermore, this leads to confusion about the cause and effect of circumstances that people find disturbing.