Sometimes talking (warning) doesn't get the job done. There is such a thing a "tough love" and what it really means is allowing a child (particularly an adult child) to experience the full consequences of a painful decision without interfering, excusing, or minimizing it. The child may think the parent "hates" them for not stepping in, but that's because the child still hasn't crossed the threshhold into accepting full responsibility for their own actions.
Your argument makes sense. But I would always want my child to know that I loved her. I would not be happy with her decision. I would let her know that I would be praying for her deliverance from that lifestyle, but that I would always love her. Also, I would not cut myself off from my child. One never knows when our time on this earth will end, or those of a loved one. I could not bear it if my child were to die and I had banished her from my life.