That's the first factor that cannot be collectively defined.

Second, nobody knows what would be best for everyone as a collective goal. There are too many variables for any overlord to capture, in creating a goal that will work well for everyone. We can all agree that ‘fairness’ and ‘justice’ are good things, but we do not all agree on the precise content of these ideals or how to allocate scarce resources in pursuing them. Two examples: we can all agree that ‘education’ for children is paramount, but disagree on the institutional form that education should take and how it should be funded. We all think good jobs are important for workers, but disagree on the precise characteristics that make a job attractive.
 
Therefore, while most people would agree that government plays an important role in preventing social conditions from descending into anarchy, it is wise to defend the fullest possible scope for individual liberty. 
 
A basic aspect of being human is being able to live your life the way you want to (subject, of course, to not killing, stealing, cheating, or expecting other people to fund your choices). A key component of individual liberty is economic liberty. This is the freedom to decide certain economic questions for yourself: what Tomasi describes as ‘liberties of working and owning’. Freedom to decide what commercial activities to get involved in, to negotiate your own terms and conditions of work, to decide for yourself how to spend your money, choose what to keep for yourself and what to give away to causes that you want to support. 
 
You can immediately see that these are questions that other people will have strong opinions about, and if your view of these things does not accord with the majority perspective there is a grave danger of being compelled to live your life the way other people would like you to live it. 

In modern society, a ‘free society’ has gradually come to mean a society in which noble ideals such as equality and distributive justice are so important that of course they should override individual liberty because, after all, what sort of individual would oppose such virtuous ideals? Probably not the sort of individual we should be too concerned about thwarting as he tries to pursue his selfish goals, it would seem. Yet while social justice ideals are attractive in theory, they have pernicious implications for individual liberty.

One reason why it may seem justifiable to abrogate individual preferences in favour of the public interest or collective good is the revulsion many people feel to the notion of 'selfishness', hence the idea that other people should be forced to prioritise the public interest if they fail to achieve this moral standard of their own accord - the idea is that it's all very well to talk about freedom and liberty, but if you come across somebody being selfish and refusing to share their stuff nicely with others you should by all means set them straight by force if necessary. Freedom is reserved only for those who exhibit generosity of spirit and choose a life path that will be pleasing to others.

Another reason is that the scope of private decisions is these days very narrowly defined. It's ok to make private decisions about what to eat for dinner, or what to watch on the telly, etc, because that probably affects nobody but yourself if you do it in the privacy of your home where nobody will ever hear about it, but anything that will affect your neighbours, such as being massively richer than them, which will make them feel bad, consumed with all that envy, should be forbidden. Being richer than others is actually very antisocial, when you think about it, and it's amazing that it isn't outlawed in this enlightened age.

99% of working people in Tanzania are employed in the 'informal economy'. You might think that an economy which engages 99% of a country's workers should simply be called 'the economy', but the term 'informal' is used by development artists to distinguish the type of economy you find in Tanzania from the type of economy you find in, say, the UK. Undeveloped economies are 'informal' because they operate outside any formal legal framework, whereas in an advanced economy like the UK you can't really do anything, can you, without first consulting your expensive lawyers and having them brief you on a whole bunch of government rules and regulations.

To say that the government should Do Something to fix the challenges of the digital age, or that we need a New Law to control the robots before they steal all our jobs, rests on the assumption that the government knows what to do and how to do it; and that our brilliant lawmakers know precisely what law would be most appropriate and effective. 

Technological innovation yields prosperity, but alas people do not progress at the same rate. Thus, economic growth also brings inequalities of fortune. Many people would prefer to stop others from striding forward, to ensure that they are not left behind. Obviously nobody likes being left behind. It's difficult to know what to do about progress because, as Angus Deaton puts it, we want to celebrate the ‘great escapes’ made possible by innovation and growth, but we also want to have regard to those who are still lagging behind: the ‘great left behind’. 

​The ultimate goal of one’s working life is to achieve individual prosperity and wellbeing. This is most effectively sustained through free markets constructed upon the ideals of economic liberty, with the role of law limited to ensuring free and fair competition, protecting property rights, and enforcing contractual obligations. 

The Court of Appeal has just announced its majority opinion that drivers who work for Uber are...well...Uber's workers, and so they have the same rights as other workers (essentially, claims to the minimum wage and paid time off). The courts have arrived at that conclusion by applying the duck test, i.e. if it looks like a duck and quacks like a duck and waddles like a duck then it's absurd for Uber to argue that it's not a duck. By this reasoning, most people would say that Uber drivers are definitely workers because there we see the drivers, working hard, driving Uber cars, and Uber is making a lot of money off the sweat of their brow. That clearly means they're working for Uber, right? ​

Everybody knows that if you ever have an idea about something that would be really cool to try out, the first thing you have to do is hire a lawyer to give you advice on how to achieve your dreams. Conventional wisdom is that it would be too risky to try and achieve anything without legal advice, and absolutely foolhardy even to attempt anything when your lawyer has told you that you're probably going to fail because <legal this legal that>. I would like to disclose a truth well understood by anyone with even the slightest insight into the functioning of legal systems: law is trivial, my friends, and of all the things you need to consider when planning a business venture the law should be the least of your concerns. I refer, of course, to the private law that regulates private transactions between consenting adults. [Editor: 'private' in this context has no salacious connotations; it means transactions not involving the state or government]. 

By now it has become quite rare, in our highly regulated world, to come across the old-fashioned phrase 'freedom of contract'. Occasionally this concept crops up in debates about why we have to follow regulations we don't agree with. This doesn't often happen: we have a come a long way since the ancient golden era of freedom of contract. But occasionally, when you're innocently and quietly reading a Supreme Court decision on why it's wrong to charge people fees to file complaints against their employers (surely anybody should be able to complain about other people for free?) you are suddenly and brutally confronted with the idea that notions of freedom of contract might actually be relevant to this situation.