Should the United States be the world's policeman? No, it should not. There are many convincing reasons why it should not undertake this role.
First, is the United States trying to spread freedom throughout the world? This goal is illogical in view of the fact that many countries already enjoy more freedom than Americans do. According to the most recent report from Freedom House, many countries rank higher than the U.S. The list of countries with more freedom include Canada, Japan, and France, among others. America's brand of democracy is not the best. Because the U.S. is not the freest, it can hardly claim to be the world's policeman for freedom.
In fact, personal freedom in the U.S. has declined under President Donald Trump. Nevertheless, he selectively upholds freedom abroad in certain cases, such as Venezuela. Meanwhile, he has openly professed his admiration for numerous dictators.
In addition, the U.S. simply cannot "make" a country free through military force. In the past two decades, the U.S. has spent trillions on combat in—and the occupation of—Iraq and Afghanistan. Those two countries remain corrupt dictatorships, in spite of America's investment of so much treasure.
There are practical advantages to not being the world's policeman. For example, the U.S. could greatly reduce its defense spending and use the savings in the U.S. to upgrade its crumbling infrastructure.