Let's imagine this scenario: Those crates needed to be rented for the game. The shortest kid demanded that the tallest kid pay for one of his crates. Is this fair and just? It may be kind for the tallest kid to offer to pay for one of the crates, but should he be obligated to? This is more like the real situations that this image is used to represent, for example, wealth distribution. Do we tax the rich more so that we can give more to the poor? In real-world situations, we are taking something of value from one group, and giving it to another group. There are many good arguments for wealth distribution, but the term "equity" refers to fairness, and many people have a problem with the idea of taking from the rich to give to the poor as representing "fairness."
Uncomfortable Idea: Equity is synonymous with fairness, but not with wealth distribution or giving people who don't have a lot of stuff, free stuff. While there are many good arguments for wealth distribution, there are also many good arguments against it.