Our bonus scheme pays out more if we haven't had any days off sick. Is this right?

Such schemes hide the real level of workplace sickness and should not be accepted. Going to work when you are ill can lead to accidents and mistakes, potentially spread your illness to others, and ultimately lead to a loss in production and efficiency. It also creates a lack of respect for the organisation and leads to a high turnover of staff. People might even overuse medication, which could lead to even greater health problems brought about by dependency. 

This kind of scheme can also discriminate against disabled workers, whose disability can mean higher levels of sickness absence.