It's actually kind of inefficient to gather negative emotions this way. If it actually did absorb them to grow stronger, merely existing inside of almost any city would be more than enough to make a negative energy creature grow in power quickly. Cities by their nature are groups of huge amounts of people, especially in China, and even if the percentage of people experiencing negative emotions is low it would still dwarf the volume of produced by 20 miners. You wouldn't need to be evil, you could travel and passively absorb tons without deliberately harming others.
