"Sinful" used to mean something immoral.
Today - it doesn't mean that anymore. Immoral is the standard. In the outside world - who doesn't sleep together before marriage? It is completely accepted to live together and have numerous children before getting married. If one is inclined towards the same gender - well then that is something to be "proud" of. Not a sin. If you say or believe otherwise then you are a fanatic.
So what is "sinful" today?
A rich, sugary piece of chocolate cake. THAT is sinful....
AHHHHHHHH!!!!