I don’t see the point in continuing this, but buying and selling are the foundation of every economy. The fallacy that one party wins by selling at the expense of the buyer is a central theme in the works of both Mises and Rothbard. This fallacy only holds true in cases of involuntary exchange, where coercion is involved. In voluntary trade both parties exchange something they value. The merchant receives Bitcoin, and you receive the product - both sides benefit.

Now that you’ve spent some Bitcoin, you’ll eventually need to replenish it to buy other essentials while setting some aside for savings. That puts you on the demand side. The merchant, who now holds Bitcoin for future expenses and possibly for savings, is also on the demand side. Before this voluntary exchange, only one party was demanding Bitcoin - now there are two. Work out the rest by yourself.