Today's society presumes the existence of free will. Otherwise, how should punishment be justified if I'm not really responsible for my actions? How can democratic decisions be fair if people don't act on their own behalf but can be and are in fact influenced?
So, free will is one of the corner stones of free societies. The promise that everyone has the liberty to do what they want, unless it impairs other people's liberty, as well as, beyond basic liberty, the democratic principle to choose the action that most people agree with, both rely heavily on the notion of free will.
The question of the existence of free will is thus not just a theoretical problem for philosophers but rather a mystery the solution of which could have quite real consequences.
Why is "free will" an oxymoron? Let's consider what "free will" actually means.
Always learning: "The will"
In order to take a closer look at the will, your every-day machinery of taking action, we need to delve into psychology, specifically the theory of Behaviorism. Behaviorism is currently the theory of the mind with the best results in the real world: Behavioral therapy helps and has helped millions of people deal with anxiety, depression and other problems. Thus far Behaviorism could be regarded as the most successful model of the mind.
In essence behaviorism views the mind as a function that applies past experiences on new experiences to produce behavior: Let's touch the hotplate! The results of this behavior in turn add to our experiences to produce maybe the same, maybe a new action the next time: If I burn my finger on the hotplate, I might try touching it again a while later but after having been burnt a second time, I've definitely learned my lesson. This learning effect is a crucial element of how our mind works.
But how do we decide which actions to repeat and which to cease? We in turn base this decision on learned knowledge and of course on our basic instincts of self-preservation and reproduction as the ultimate origin of our behavior: We just know that "Ouch!" is not an experience worth having and thus cease to touch the hotplate immediately.
There is of course a multitude of decisions which are much more complicated than not-touching-a-hotplate mostly due to a conflict between past evidence, knowledge and/or our instincts. Which evidence, piece of knowledge or instinct wins is mostly due to learned experiences but also to genetics: Just like some people are more rational while others have a temper.
So, the simple conclusion is, as you probably knew all along, our decisions are based on how we were born as well as what we have been taught by life, while the exact amount of influence of these two factors is still hotly debated.
The void: "Freedom"
Freedom is, short and sweet, the state of autonomy and isolation from outer influences or constraints. Freedom is always a compromise and never an absolute state. One can only find true, complete freedom in death, which is not usually desirable.
Putting them together: Burger or salad?
So, when we look at what "free" means and what "will" means, "free will" would mean that I'm isolated, uninfluenced and unconstrained in my decision-making.
To test, whether this makes sense, let us consider an arbitrary decision: For example, I get the choice to eat a salad or a burger. If we consider only the moment of the decision, then the decision should obviously be free from any outer influences, right? After all, nobody is holding a gun to my head, forcing me into a specific decision.
However, when looking at how we make decisions, namely how our decisions are based on past experiences and instincts, it's clear that we cannot disregard time like this, because if we were isolated from all our experiences, what would we base our decision on? How would we know whether to choose the burger or the salad? The decision would be meaningless and random. Without my past experiences, I'd probably tell myself, "I don't know. Whatever!", as both having seen a burger and a salad is a past experience I wouldn't be able to remember, just like any information I might have gathered about the two.
"No", you say, "I'd choose the burger, because it smells better!". Does our instinct save the concept of free will? We are, once again, disregarding time (and perhaps biology). Our instincts are mostly inherited from our parents (they could also be the result of genetic mutation, which however also happens due to outer influences). So, as my genes are determined outside of me, without me having any influence over them, are my instincts are also isolated, free from outer influence? Not really.
I simply cannot decide without my past experiences, my knowledge and my instincts, which are not free from influences, and thus the concept of "free will" is a contradiction in terms and doesn't make sense: We are where we come from. Beyond that there is nothing in us.
What are the consequences of this realization for today's society? Identity is key to everything in our society. It's what drives our emotions and our behavior. Thus, everything, from our social peer group, our consumer choice over political stances to court verdicts is based on identity.
However, as we've come to realize earlier, identity is based on what we've learned and how we're wired to learn. It is not set in stone, but the rules of society treat it like it is. We judge other people on their opinions and actions, we punish them for acting on their beliefs and fears. E.g. By reducing someone to their sexist world view, we actually reinforce this identification and incite fear that will only lead to a more firm belief in what the person identifies with. We try to fight people with unhelpful beliefs, when instead we should help them fight the beliefs themselves. Education instead of ostracism and punishment is the important keyword here, especially as an answer to the currently thriving right-wing movement in Europe.