Our mind may speculate over an extended variety of subjects.
We may speculate that maybe we are just the result of what happens inside our body and brain, we may speculate that maybe we are just a brain in a vat.
We may speculate whatever we want (if we are free), or whatever we have to (if we are not).
We may speculate that we are free, and we may speculate that we are not.
We may speculate that all the existent is determined, and we may speculate that is is random.
It's all ok.
Actually, we are spiritual beings, single human consciousness living in a universal network of consciousness. All the existent is not determined nor random, but the fruit of an intention.
I won't speculate about this matter, because this is something that we have to experience, not to speculate about: Truth is an experience, not a theory.
If one wants or needs to believe in some theory, instead of experiencing reality, he is free to do that.
But, if being deterministic, or materialistic, leads to:
In this case a speculative theory has become something different: it is now a mental illness.
One can go on speculating that this is not true, but this would lead just to worsen his experience of life.
From this perspective, if we really have to believe on something (I am not suggesting to do that), we could believe that:
For my experience, experiencing something is always better than believing. But, if we really need to believe in something, why don't we start believing in something that enriches and elevates our life experience ?