Thoughts as I contemplate their situation

I have been subbing for a teacher who has 9th and 10th graders with the age ranging between 17-19 years old. Of these 11 students, some are no longer eligible to receive credit for the semester due to unexcused absences, yet they come to school each and every day. One might think, "wow, talk about dedication!" Sadly, they do not come to do assignments, nor to do any work at all... Today after ruining their day yet again because I told them, "When you come in to the classroom as a student, it is automatically assumed that you are here to do the work for that class." Previously, I told the student if they are unwilling to do the work, they can leave. I received a prompt "You are supposed to encourage, not discourage students!" along with a few mumbled threats. I replied, "I am encouraging you - to do the work you need to complete to pass the class." Today I went a step further. I told the students, "If I am saying anything that you do not like, please write down the words I need to say in order for you to become a successful student so I will know what to tell you. I need to know what words need to be said for you to realize you need to do the work in order to earn the grade. School is just like a job: if you don't do the work you don't get paid. Your grade is the payment for the work you need to do each day. I do not know of any job that would pay anyone for doing nothing." The end result was that I still had the same students sitting in my classroom. However, today they were not as distracting to the rest of the class. I know this is not the only classroom that encounters this dilemma. I know it will not be the last I have - although with my elementary degree hopefully I will not encounter the aforementioned circumstance in the future. What I cannot get is the attitude that it is my fault. I am the mean teacher who forces them to think on their lack of motivation... Sorry - I just needed to vent... still... no solution... still end up with kids hanging out in class, doing nothing...