Free will is given for us to rise above our animal instincts. So lets examine this against your 3 steps, but there needs to be a 4th, which is indeed the first step.
1 - First what determines what is an evil desire? What are the set boundaries, mans laws or Gods Laws? Nature and Nurture for each person would define these and one would presume that the person making the choice, has already had an education that defines the Moral Boundaries. The education given should have given us the skills required to suppress animal desires for higher goals and for the good of all peoples. This is best done with the Spirit of Faith.
"1. The person has an evil desire." This is the seed to activate free will, the chance to make a positive and good thought override the evil desire, at this stage we have the choice to replace this evil thought with a thought that is good.
2. The person chooses to act on their evil desire. This is the Free will Choice. When Nature and Nurture Had set the boundaries and told of the consequences of neglecting those boundaries, then this is man giving into his weaker side. If Nature and Nurture has neglected to give the boundaries, then we have to ask what was the boundary crossed?
3. The person causes the evil desire to happen. Could we say the cause was actually before this, the cause was at your step 1 when the seed of the evil choice was not replaced with the seed of a better thought. Could it be the thought is already the act, even if not to the stage of acting upon it in each individual. By harboring the thought, we feed others that are weaker to undertake the act.
In life we must consider to take all evil out of all our thoughts and not in any way feed the desire to do what is not good.
Regards Tony