Without the temple and access to the ritual of the red heifer, we're all tamei (ritually impure) today with no way to fix it. Yet we work to avoid situations that would make us tamei (e.g. kohanim still don't go near most dead, aside from close relatives). Why is this? Can one become "more" tamei with each exposure? Or does it not have anything to do with our state but, rather, is about not developing bad habits that will be hard to break when we do have a third temple?