Depends on the work. If it were like a soviet-style gulag as some emotional people might immediately point at that would be bad, but having some form of regular involuntary labor system would be much more humane than what's going on in our prisons currently, and for less severe or especially juvenile offenders the experience could be helpful for finding a job after they get out.

Prisoners do in fact work to pay for their prison fees.

Yeah like people said they do that already. I don't agree with them doing too much work though, because even if sewage and construction don't sound appealing people make a living doing that stuff. You wouldn't want new free labor in the form of convicts taking their jobs.