There are several reasons why I hate the Imperial system:
The biggest reason is that the imperial system has absolutely no pattern between the units. For example, 12 inches = 1 foot, and 5280 feet = 1 mile. There isn't a pattern to be found, and this makes the measurments very hard to remember. It is so overly complicated and makes zero sense.
There are way too many different units in the imperial system. With this system of measurment, there are many different units (feet, yards, miles, etc.) for each of the kinds of measurment (weight, length, volume, etc.) These are even more words you need to remember. With the metric system, as long as you know the prefixes (milli-, centi-, deci- etc.) and whatever unit you need, you don't need to memorize a million words when converting or using.
For some of the units, there are several different values. For example, ounces, fluid ounces, and troy ounces (used for measuring precious metals like silver and gold.) They all contain the same word: ounces, and that could possibly cause confusion when remembering what each are worth.