While I think that detention should be used for more serious violations of school rules like disruptive behavior, or as a step in progressive disciplinary measures for students who present repetitive behavioral problems, using it as punishment for not turning in homework is a bit extreme.
However...
we cannot continue to reward our children for doing things that are already expected of them as suggested by "mykidsmom", otherwise when they make significant accomplishments, the rewards will be meaningless.
There is nothing wrong with an Attaboy once in a while or telling your child how proud you are of them, but face it, the rewards and praise lose their effectiveness as incentives when given all the time (leaving us searching for ways to "top the last one" and thus creating a society of materialistic, spoiled adults who think they should get a raise just because they show up to work on time.)
Cruel though it may sound, children need to understand that there are consequences for their lacking to do what is expected, and we as parents have a primary responsibility to enforce that in our homes and support our schools when they enforce it there.
There is always a compromise to every situation, though. Talk to school administrators, Board members and your district's superintendent. Get a copy of the entire policy (as public record you have a right to this information) and read it three times. Discuss it at your next meeting and gather input from teachers, parents and administrators. Ask about modifying the punishment from detention to, say, recess detention, being kept behind from art or gym class, or using homeroom time to complete the work. Then take 10% off the grade for turning in late work (did you ever get full credit in high school for turning in a late paper?) Ten percent off is certainly better than getting no credit at all.
Teachers will know who the "repeat offenders" are and be able to determine if domestic or other circumstances are hindering those students' academic efforts or if it is just plain laziness that prevents a student from completing his or her work.
Are there tutoring or mentoring programs in your school that at-risk kids can be enrolled in? If not, why not look into getting one started (a point of advocacy from your PTO). If you are in a middle or elementary school, check with the high school guidance counsellor to see if students there can become tutors or mentors in exchange for community service credits (most states require the completion of a certain number of community service hours for graduation). Your local senior center, fire department, churches, and scout groups are other great places to tap for tutors and mentors.
There are a number of questions to ask before one attacks a policy aimed at teaching the children personal responsibility and the importance of following directions. Imagine the society in which they would live if they aren't taught those skills.