It's the workers who have been shafted by declining standards of living, stagnant wages, rising prices, false promises about the benefits of free trade agreements, and increased immigrant labor -- coupled with an increasingly bureaucratic EU organization that pushes more political change than economic/trade change. The citizens of Britain signed up for the EU when they saw it as a trade agreement that would benefit them down the line, instead they are giving up more sovereignty to EU's bureaucracy in exchange for benefits that disproportionately flow up to the elite.

And it's not economic suicide. In the short term it will most likely hurt but in the long term, Britain will survive and the EU will need to bend to accommodate Britain's consumers, even if the UK is not a member state. It is one of, if not the, biggest importers of EU goods and it's the EU, not Britain, who cannot survive without accommodating the other.

Also I don't see why the US would benefit in any way from a collapsed EU or UK. Trade and travel becomes harder when they are not a single unit.