Rampant? 4800 issues reported in BC over a 5 year period[1], in a province with over 20,000 community mailboxes. Issues include non-theft things like graffiti and other vandalism. Haven't found more detailed info, would appreciate a link if you have one.
1: http://www.cbc.ca/news/canada/british-columbia/super-mailbox...
The level of audacity it takes to assault and rob a government employee, versus casually walking into someone's driveway and grabbing their mail are not even close.
I have people delivering fliers to my mailbox multiple times a week. It would take no effort for them to grab my mail and stick it in their sack.
But again, I don't think "the ease at which your mail can be stolen" should even be part of this argument, as it's apparently significantly low in most cases.
Suspiciously door-to-door? Slap a newspaper bag over your shoulder like you're delivering fliers and go collect everyone's mail.
Quickly retrieve their mail? Most people are at work for hours before and after the mail is delivered.
I've lived in communities with both services. I prefer home delivery, because it's more convenient to me. But if you think it's easier to break into the super-boxes than it is to steal someone's home delivered mail, you're out of your mind. Luckily, community morals make either mostly a non-issue.