Yeah. The main reason I feel a need to believe in free will, is because if I assume a perfectly deterministic world, how do one defeat the following question:

Yeah. The main reason I feel a need to believe in free will, is because if I assume a perfectly deterministic world, how do one defeat the following question: Why is it worth putting any effort in? In a perfectly deterministic world whatever will happen will happen. Me deciding to just not try won't change anything, since me doing so was predetermined in the first place. That argument is pretty trivially defeated by believing the concept of free will. (Even if this belief is false). And yeah, I know the previous argument is deeply flawed, but giving a satisfactory counter argument not based on free will is tricky at best. This ties deeply to the concept of illusion of free will. If you can conclusively and convincingly prove that there is no free will, you can lose some of the benefits of the illusion of free will. For example, if hypothetically one were to prove that the world is fully deterministic, and no free will exists, then it opens a bunch of other philosophical questions. Is it right (moral) to punish people who commit crimes? If the person were pre-ordained to commit the crime, and could never have actually prevented themselves from doing it, can they really be blamed? Obviously, if somebody has a faulty brain that makes them more likely to commit crimes (and has shown this, by committing said crimes), then locking them up to protect everyone else might be reasonable. Trying to rehabilitate them (i.e. change the inputs of their deterministic though process, such that they would not do the same in a similar situation in the future) is also reasonable. And perhaps punishments as a deterrent mechanism might still be valid. But I really have to question if it is actually moral/ethical to punish somebody for something if they truly had no choice in the matter. It seems as society we feel the answer might be no, as we choose not to punish people who are incapable of understanding that what they did was wrong (like young children, or those deemed legally incompetent/insane). This is generally also true of animals, which are usually not punished for doing something we deem as "wrong", but instead are often relocated, or killed (not as punishment, but to prevent further danger, since giving an animal life without parole to protect people is not deemed viable). This is only one of a whole list of philosophical questions we would want to revisit if we truly knew free will does not exist. I go with a deterministic universe above because it simplifies the arguments. A non-deterministic universe in theory could have some of the same difficulties, but it is harder to formulate the relevant arguments.