I find it puzzling that Christians in particular seem to be irritated by the idea of a lack of free will.
More than once I've seen a religious person irritated when the notion of determinism came up in a discussion.
What is the connection there?
People become irritated for many reasons. However, one possible reason is because determinism is a subtle attack on them and on their beliefs. They may not be able to articulate the attack, but recognize that it is one. They may not even be able to mount a defence or counter-attack and feel frustrated without understanding why.
Christians are told that they must a) Have faith and b) choose to follow Christ. (Many Christian sects differ on the definition of "follow Christ", but they all state that it must be done.)
If there is no free will, how can one have faith? How can you trust someone to reward you for your actions if your actions are meaningless? People choose to "follow Christ" in hope of a reward. By taking away free will, you are taking away their hope of a reward.
Determinism basically calls people stupid for making the choices they did, as well as takes away their hope of an eternal reward. Is it really surprising that they get irritated?
Isn't it conflictive to believe in an all-knowing and all-powerful deity while at the same believing in freedom of choice?
Not really. If there is an all-knowing and all-powerful deity, there must be a reason why we are here. After all, if this deity already knows who will be rewarded and who will be punished, why aren't we already in Heaven or Hell? If nothing we do makes a difference, why are we made to do anything at all? If you accept an all-powerful, all-knowing deity, then you must accept that there is a reason we are here. One possible reason is that we as individuals are important to this deity, and that we gain something by going through this experience. If we do learn and grow by making choices, it follows that this deity could allow us to make choices, even if the results of the choices were known in advance. Knowing what someone will choose is not taking away their choice.
Some people believe that an all-powerful, all-knowing being is forced to manipulate the out-come of all choices, thus removing free-will. Others believe that the same being is free to choose not to manipulate those choices. Thus, to them, an all-powerful, all-knowing being does not conflict with freedom of choice.