"They" aren't wrecking the system, so much as the inherent flaw in the system makes it inevitable. Email costs a negligible amount to send and there's no way to reliably control the overall system.

It's not a problem in isolation, either. The bigger issue of systems that no longer meet the definition of economic scarcity is growing. Scarcity has always been our way of controlling abuse by excess, but many things are becoming so cheap as to negate this method. We need to build other methods into our World.

Some systems that have dropped dramatically in price, such as phone usage minutes, haven't become a problem (much). Others, such as calories, have become severe ones. Email abuse didn't hurt much else, but it's nearly ruined email itself.