There is a distinction between being a sinner, which we all are, and being faithful to the Church. Being faithful to the Church means obeying the teachings on faith and morals. There is a huge difference between drinking, which in and of itself is not a sin, and blatantly refusing to believe or be obedient to the teachings of the Church. To be a faithful Catholic means that a person is humbling themselves to the teachings of the Church because you believe that the Holy Spirit guides the Church on its teachings. If you don’t believe that (ie you don’t believe contraception, homosexuality, pre-marital sex, or any other teaching), then I would presume that you are not a faithful Catholic.
A person can sin (drink too much, lie, contracept) and know that it is wrong but in their human weakness commit the sin anyway and still be a faithful Catholic. However, you cannot sin because you do not believe it is a sin and be a faithful Catholic.