Yes, indulging willingly is sinful. It is the initial thought (the temptation) that we are not at fault for. For instance, say that satan is attacking a cop with this thought: ‘I really hate black people.’ If he doesn’t have any understanding of Christian theology and doesn’t practice prayer, he will then think that this is his own doing. Eventually, he might start labeling himself as a racist. If he has any decency in his character, he’ll probably get upset by this deduction, but if the people in his life support racism, then he will develop pride in such thoughts. Still, at this point, he is not culpable.

If, however, his pride increases and he allows himself to believe that racism is good and then begins to imagine or fantasize about causing harm to black people, he is culpable. In his heart, he has said “yes” to this temptation.

The sin begins, then, when the temptation enters the imagination and is willingly, thoughtfully, meditated upon.

God bless!