Why are people on here so anti-futurity?

I cannot hold an opinion on futurity as I do not know what it is! But I guess it might be to do with breaking in and showing horses at a young age. We in the UK wait until they have had their big growth spurt and then back them at 4 and turn away for the next few months to mature. I do notice that you are breaking horses in in the US far earlier, and I guess this is why people might be upset by this as horses muscles and skeletons are not fully formed and are soft to allow for growth.