you definitely have to love words to go into editing as your main source of income. granted my editorial tasks are more geared towards small business blogs (pest control, start up law firms, catering companies, etc.), i still run into a lot of the issues that you're stating here.
it's a labor of love for sure, though i don't know how well i'd do with editing a writer's book as my day job. i know we writers are fickle, fickle creatures and, too often (myself included), we LOVE our little darlings and refuse to kill them based on...what? ego? pride?
either way, that's gotta be a tough call sometimes, telling an author you can't move forward, even if all the issues are glaringly obvious and in desperate need of fixing.