Your whole premise seems to rest on the belief that people won't risk a felony conviction for something they feel strongly about. I find that belief to be rather naive.
Your premise is that somebody would have the knowledge to know whose mailbox to steal from. When to steal from it, and to get away with stealing from it, without anybody (such as neighbors) noticing somebody suspicious going from house to house, looking in the mailbox.
Of course, sending it to the persons last known address, may very well mean somebody else is living there, and they don't mind a stranger rummaging through their mailbox.
I'm not saying it can't happen, but to do so on any large scale basis, the odds are somebody would have gotten caught doing it. And nobody has been caught doing it.