I don't understand why anyone would do it with an FZ6, but it's not that uncommon for larger touring bikes. If you ride tons of miles (IBR types) on a heavy bike with lots of gear, you're going to eat a lot of tires. And those riders are primarily traveling on slab at high speeds. Handling isn't really an issue.
One of the main selling points of the FZ6 is its handling. And its relatively light weight and small displacement engine keep it from burning through rear tires too quick. Add the fact that it has a sub-par stock seat and wind protection, and I think it's clear there are significant obstacles to long-range trips. It can be done, but it's not a great platform to start with.
As for your friend... don't bother trying to understand someone who rides a cruiser. He wants different things from his motorcycle. It might be a decent set up for him. I mean, it's not like he's losing much in handling. His bike barely leans over at all. Maybe HD will come out with a "Darkside" lineup next year? Sounds badass. Who cares how it actually rides, right?