They are classified as bad because of many different reasons. But since this topic is about dps, bad players generally do not know how to execute a proper opener, basic rotation, opener mid-fight. How to recover after a death? Do I start my rotation from where I stopped or start over? Every job is different. If they did know their basics, you won't see their dps falling below Average.
You are doing content with PF, and like I stated before, you will hardly ever run into good players there. Don't assume that what you run into is the average.
A job is designed to deal a certain amount of dps. If a player is not able to meet these numbers then they are playing the job wrong. Why would you defend them?
Logs show them where they stand. Rather than playing victims, they should aim to get better. At least meet the average requirement and no one will say anything to them.