This is the essence of a free market – it is voluntary – it is not the government making you (or the government empowering some other entity to make you) buy or sell or determine the price at which you must buy or sell or punishing you if you do not do what the government (or a government sanctioned entity) wishes for you to do.
This is called freedom and this is called a free market.
All other economic/political/social systems in which the government requires you to buy, sell or determines at what price you will buy or sell, or punishes you for not engaging in commerce which the government sanctions is not a free market.
The adherents of Bernie Sanders and Elizabeth Warren are not going to come out in their campaign propaganda and say “We will use the force and power of the government to make you buy, make you sell and control the price at which you buy and sell and punish you if you do not do what we wish” but that is exactly what their policies will do.
Using the power of government to make you buy, make you sell, determine the price at which you must buy or sell and punish you if you decline to participate is what their entire political platforms are based on. They hire very bright people to decorate this idea of using government force to compel you to enrich the private entities that donate to their campaigns – using words such as ‘fair’ and ‘justice’ – but at the end of the day it is simply using government force to transfer your wealth to their supporters. End of story.
You have two choices here – you can choose a free market in which each individual is equal, no one can compel you to engage in commerce which you do not wish to engage in, and no one will use government force to take your wealth and transfer it to their cronies – or you can choose a system in which some politician will decide what is equal, the government will compel you to engage in commerce, the government will determine what commerce at what price and in what quantity you must engage, the government will use force to take your wealth and give it to their supporters, and freedom continues to die.