Why it is better when two firms compete?

It is good for two firms to compete, especially for the consumer. The best way to show this is by a basic example. If Company A is the only company that makes TVs, then they can charge whatever they want to because they are the only company that makes it. If Company B begins to make TVs, then Company A now has competition. Now, Company B could price their TV lower than Company A, and in return, Company A has to price theirs lower to keep up with the competition. Now, in today's world, throw in multiple competitors and that is what the economy is made of. It is great for the consumers, but bad for the firms because they won't make as much money as they would if they had a monopoly. The Sherman Antitrust Act was put in place to protect consumers from monopolies taking advantage of them.