Your essay on the ethics of street riding has nothing to do with the Hi-Tensile steel vs. 4130 Chromoly debate.
Nevertheless, street riding IS a major part of BMX. So to claim that BMXers would be fine w/ Hi-Ten based on a series of youtube clips you've culled from Dew Tour riders simply shows your ignorance of what BMX riding fully entails.
Sure, Hi-Ten would be fine for entry level riders just starting & wanting something cheap. But at a higher performance level, we want something stronger, lighter, simply better.
You can make a stronger frame at a lighter weight using 4130. And that's what we want, light yet strong.
For High-Ten to be as strong, you need more. Thus heavier.
-Bill