A fundamental principle of economics is that if you force an exchange rate that doesn't match what people really feel, you will create a scarcity of the undervalued item. If, for example a guild forced a 2:1 ratio of LMA:Colonial, while most people felt the 1.5:1 ratio was closer to fair, would tend to find few people offering LMA goods for Colonial, and people offering Colonial Goods for LMA would likely find their trades taking longer than normal to get accepted. Some trade would still occur, as different people, in different circumstances do have differing values, and there will be some people with LMA goods with a strong need for the Colonial goods (or a sense of egalitarianism willing to be helpful) to make the trades at those ratio.
The Equal Value ratios may be reasonable in many conditions, but are in no way perfect. For example, trading up from Industrial to Progressive, the 'Fair Trade' ratios seem to underestimate the value of the Progressive goods, in part due to the need for 2 lane roads makes them especially big in comparison.
At lower ages, the fair trade ratios seem real close to what would generally be considered a good ratio, and establish a reasonable baseline for trade. I think the real idea that started behind the concept of Fair Trade, was to exclude those doing predatory trades,like 1:1 going up an age of 2:1 going up a couple, not with the idea that the ratio was 'fair', but hoping someone doesn't notice that it is a really bad deal. Others seem to object to the concept that someone might be able to profit from the needs of others, doing something like offering at a slight markup goods that seem to be scarce.
