How were monopolies considered evil?

Monopoly business refers to the only provider of goods and services without much competition prevailing in the market.

Explanation:

There are many drawbacks in such business ventures. Monopolistic dealers are the lone providers of the goods and services and hence they are independent to fix the price regardless of the demand of the goods. Gasoline and petroleum products are some examples.  

The quality of the product may also be decreased when monopolies exist and the consumers unaware of the trademarks that is provided to the goods. Lack of innovation is another great evil. People tend to stay in the comfort zone than to innovate and create something new. Monopoly curbs the aspect of innovation in the marketing of the product.