Why should the definition matter at all?

Americans typically use imperial because it plays nicely with most other things in the US that use imperial, not because of some vendetta against the metric system. As easy as the metric system may be, it's a lot harder to use a different system than almost everything around you.

I count 2 halves, halved and quartered.

It's largely a solved problem: you sort of just bury it very deep in a geologically stable area.

Yes, there is some risk of toxic material affecting something, but it's not nearly as severe as the guarantee of toxic material getting released with fossil fuels.