Not having a free will does not mean that we don't have social constructs of responsibility, standards, expectations, obligations, duties, agreements, or contracts. The fact that we can expect things of people at all is another example of determinism.

What it does mean is that these expectations are all forced upon us just like our existence and that we cannot logically credit or blame people for their conformity to what we expect. This is important for us to understand to reduce hatred and violence. I feel an obligation to act in a way that I believe is the most moral way. Since my will is to create a happier world, I cannot stay silent about what I think will lead to that outcome.

If I am the only one who can say or do something, doesn't that obligate me to do it?