This thread is a year old, but I'm going to add to it anyhow. I'm not actually replying directly to the original question: Why do conservatives dislike the metric system? Instead, I'm going to make some observations.
0. The formal, full blown metric system is often known as SI, from the first two initials of it's French name.
1. The SI is about measurement. If you do little measuring, it doesn't really matter to you. Most people do not measure often. Those people who use measurement extensively find SI very helpful. The biggest advantage comes when measurements of different physical properties have to be combined. SI is specially designed to help ease these operations.
2. The complaint that resonates most with ordinary people, who do not measure much, is that SI units are not "natural"; people have trouble visualizing them. What this really means is that Americans are not used to using SI units. SI are not unnatural, they are simply unfamiliar. Once one starts using them (I speak from experience), they become as familiar as English units.
3. Part of our problem with SI involves a poor choice about how to teach it. Early in the typical public introduction, we dive deep into conversion between English and SI units. Conversion is an unfortunate necessity in a world that still uses other systems, but it's not a serious issue to people who actually work in SI. Once the conversion is made, all of the measurements one makes are SI and no conversions to other systems are necessary. Emphasizing conversion adds an unfortunate, largely unnecessary, layer of complexity onto the educational process.
4. Who does use SI regularly? Chemists, physicists, biologists, biochemists, molecular geneticists, biotechnologists, material scientists, electrical engineers, chemical engineers, many (I'm not sure of the fraction) mechanical engineers, many (probably the majority by now) aerospace engineers, physicians, nurses, pharmacists, machinists, etc. In other words, people who work in fields where measurement is important, use SI. If you want your child to grow up to be an engineer, scientist, physician, nurse, mechanic, etc., don't badmouth SI in front of them, and help them learn it, because it is a vital job skill that they need to learn. If you want your child to become a used car salesman or tobacco picker, then they don't need SI and you can badmouth it all you want.
5. In addition to the formal SI, there are a host of other "metric" standards. A common example is threaded fasteners. Think about the lowly machine screw (bolt) and nut. There have been several systems for machine screws. There has never been an "English" system. There were two or three, at least, British systems and one common American system. The American system for ordinary sizes uses two incompatible schemes: Smaller sizes are "number sizes", e.g. 6-32, 10-24 (the diameter numbers are purely arbitrary, the pitch number is threads per inch). Larger sizes are inch fraction, e.g. 1/4-20. (The first number refers to diameter, the second to pitch, the spacing of the threads, in threads per inch). Metric screw sizes are similar, giving diameter and pitch, but the measurements are in millimeters, and the pitch is given as millimeters per thread instead of the inverse system used in the American and British systems, e.g. 5-1 means a screw 5 mm in diameter with 1mm between threads. American screws also have "course" and "fine" pitch standards. Metric screws mostly have only one pitch that usually falls between the American "coarse" and "fine".
Metric screws prove to work well in most applications, and we see them more and more. The most obvious place is automobiles, where metric screws have become the norm, even in the US.
Nearly all of the cost and complexity for industry to transition lies in these secondary standards, not in SI itself.
6. One feature of SI, one that has become more useful in the modern age, is decimalization. SI doesn't say 1/32 inch or 1/4 cup. Before calculators and computers, this was a slight drawback to people used to mental arithmetic shortcuts. Even back then, technical professionals used decimal arithmetic. Those slide rules that old timers natter on about were and are decimal calculators, not fractional. Some SI detractors point to the ancient systems we still use for angle and time measurement as evidence that systems based on whole number ratios are superior to decimalized systems. In fact, it's just the other way around. In order to use time and angle measurements in calculations, we have to do cumbersome and error prone conversions between the ancient systems and a decimalized system. Scientists using SI usually stick to using only seconds for time measurement (except in fields like geology where very long time spans are involved). The 360 degree angle measurement is a royal pain, but nobody has agreed on a replacement. (Mathematicians want us to use radians, of which there are 2 Pi in one revolution, but that is a computational nightmare, for both humans and machines, and nobody practical wants to give in to the mathematicians. Some engineers pushed for the Grad as an angle measurement. There are 400 grads in a revolution. It's got some advantages for mental arithmetic: quarter and half revolutions involve only 100 grad increments. The Grad hasn't caught on and isn't a formal part of SI.
7. SI units are increasingly common in US consumer products. Carbonated beverages and bottled water, wine and distilled spirits are almost exclusively sold in SI unit sized containers. Nobody seems to mind that their bottled water is 500 ml rather than 1 pint.