Question

why is pure competition considered an unsustainable system?
price differentiation is often too minimal to matter.
few barriers exist to entry, meaning that the market inevitably floods.
consumers cannot distinguish between products.
producers cannot make a profit if they keep dropping their prices.

Explanation:

In pure competition, there are many firms. With intense price - cutting to gain market share, producers' profit margins shrink. If prices keep dropping, they cannot make a profit, making the system unsustainable.

Answer:

Producers cannot make a profit if they keep dropping their prices.