Some people do slack off work. It's sort of like welfare. We're more concerned with who would abuse it, rather than who it would help, even when the benefits exceed the potential fraud.
Fair point. But if someone is likely to slack off when WFH, they pretty much can do the same at the office. It's a matter of discipline and productivity. I think one should be more concerned of managing the work (i.e. output) rather than the time or location.