In the first place, "metric system" means a system of measurement, so ours is a "metric" system also. We shouldn't call ours the English system, since the English don't use it anymore; let's call it the American system. And that other one, it was invented by the French, let's call it the French system. And, although we're one of only a few countries to use the American system, we are also the biggest economy in the world - something like 1/3 of the world's economy - don't forget that.
I had a science/engineering education, and for the first two years it was pure science. The "scientists" used the French system and tried to teach us intelligent life couldn't exist outside of it. Then I got into engineering courses, and they were all in the American system, and, guess what, it worked too.
I wouldn't mind going to one world-wide system, but it shouldn't be the French system. The French system has too many flaws. We need to create a more logical system.
On a scale of 1 to 10, I would rate the American system, maybe, 7. Then the French system would be 7.5. The French system eliminates a few conversions, like inches to feet or pounds to ounces, but everything else in nature requires conversion "factors". Avogadro's number doesn't come out even in the French system.
What's the most common measurement we make everyday? Even if we aren't measuring the length of something, or it's weight, we are constantly using time. Time is our most common measurement, and it isn't decimalized! Let's start our new world system by having ten hours a day, 100 minutes an hour, 100 seconds a minute, 100,000 second per day instead of 86,400.
But, of course, someone will argue that going to a new world measuring system will require all those countries to invest in new instrument, and we couldn't do that. But that is the same arguement used for not going to the French system.