[Broken Glass Can]

This is a form of "tough love". If Keyes cut off a 19 year old daughter with a drug or drink problem, people would be more understanding of what he is doing. Keyes (unlike the many phonies out there) believes his daughter is going down a similar path.

The easy thing would be to live and let live, but Keyes wants his daughter to grow out of what he perceives as her affliction. I know this is hard for people that don't really believe in anything to understand, and he may or may not be right, but it shows he stands up for what he believes, and cares more for his daughter's long term future than her short term convenience.