I am a Civil Servant and wir Attendance Management policy means that four days off in any six months or eight in 12 months can attract a warning. It is not the fact that you are sick it is the fact that being absent, even when covered by a certificate, means you are not at work and if you are not at work, you are not efficient.
If everyone were allowed to have months off sick wi no action taken against them, employers would need to employ more folk to cover for all the absences. If you are off long- term sick, why should an employer be forced to carry on employing and paying you whilst either paying for a replacement or asking others to do your share in addition to their own?