Duh, they're butthurt they fucked up, but also who cares if they're sympathetic?

If you want to keep the job, you should.

Look, if this works for OP and others, great. More power to them. But the reality is that, in most situations this isn't going to end up with the whole office applauding you for gaming the system and 'sticking it to the man' all whilst your manager looks on dispondantly from the background. It's going to result in a lot of uncomfortable discussions with HR and you potentially losing your job, or at the very least be given a written warning. If that's not a problem then great.

If your employee can go months doing nothing then you're a shite boss who's even worse than that employee, frankly

Sure, but that doesn't mean that the employee is not culpable as well. They have a responsibility to inform their line manager that they have no work to do. If the manager still does nothing, then great, enjoy the free time. But they should at least try. Your company expects you to be working in exchange for payment. I've seen situations where someone taking money for work they were knowingly not doing was accused of fraud. Maybe that sticks in court, maybe it doesn't, but is it worth the hassle to find out?