If the government is stupid enough to write law that it cannot enforce when applied by all citizens (and not only those with means), then we should welcome anything which will bring about the demise of those laws.
Most people agree that this rule works well in practice. Most people don't take a sick day because they don't feel 100%, even when its within their rights. If everyone decided to take Monday off because they're sick, that would be possible within the law, there's no need to provide proof you're sick. Yet, if that happened, the country would grind to a halt.
Now ask yourself, how could you implement that without eroding someone's rights and without introducing more friction?
Sometimes, you just have to assume that people are honest and won't take the piss out of the system. Or you have to introduce friction to discourage the exercise of their rights. The friction for sick leave is that you usually have to notify your employer ASAP and that you may have to fill out a return to work form.