All perfect praise be to Allah, the Lord of the worlds. I testify that there is none worthy of worship except Allah and that Muhammad is His slave and Messenger.
If the purpose of these words is to say that this thing which is a sin brings pleasure to the doer, then this statement is not Kufr (disbelief).
However, if by saying that ‘it is good’, he meant that it is not forbidden while this sin is known in the religion by absolute evidence to be forbidden, like fornication, then this is Kufr.
As regards matters on which the scholars held different opinions, such as listening to music, then the one who considers it to be lawful is not accused of Kufr, but he committed a mistake.
Such statements are objectionable and intolerable in any case, so one should deny them from those who say them according to one’s ability.
If the sayer is a Muslim, then it should be clarified to him that they are forbidden if he ignores that fact, and that they are evil, and their harms should be explained to him.
As regards a non-Muslim, he should be invited to Islam by clarifying its good traits and explaining that it is a religion that calls to goodness and forbids all evil.
It is tolerated to keep silent about some details that may repel a non-Muslim from embracing Islam until he is convinced of it.
If a non-Muslim does what he believes to be lawful in his religion, then one does not deny this from him; rather, one must invite him to Allah according to his ability.
Allah knows best.