The US has always been partially metric. Some things are better in metric. Like, for example, some kinds of standards. And money.
Some things are better in systems that have more whole divisors. Like, for example, carpentry, architecture for human beings and livestock, and arguably temperature (at least that was the argument Dr. Fahrenheit made).
People who advocate one system for everything are insufficiently versed in the things they want to command. They are kind of like Ronald Reagan claiming trees cause pollution after someone explained floral respiration to him.
The United States chose non-metric systems for certain things after the metric system was in common use, and this choice was made knowingly and logically. "Everything should be as simple as possible - but no simpler".