Well, this is kinda like complimentary condiments or whatever. Technically you are allowed to abuse it to the wazoo, but in practice it just means "Take a reasonable amount, we're not stingy". There obviously is an unspoken "we're all grown ups here" type of social contract in these sorts of things. Abusing it is going to come at the cost of the commons, and in the GP's case it did cost them the perk, so being angry at the abuser seems justified.
One of my co-workers a few years ago decided to go to Japan for 3 months, but that didn't fly with my company and it ended up being mostly an unpaid sabbatical (despite the unlimited PTO policy). 3 months later, the guy extended his stay and let us know he wasn't coming back. There were no hard rules anywhere in sight, but the way this played out seems perfectly reasonable to me.